:root {
  --bg: #000000;
  --surface: #121214;
  --surface-raised: #1c1c1e;
  --surface-soft: #2c2c2e;
  --cream: #f5f5f7;
  --cream-muted: #c7c7cc;
  --cream-dim: #98989f;
  --line: #2c2c2e;
  --line-strong: #48484a;
  --orange: #eb4023;
  --orange-hover: #ff5437;
  --orange-pressed: #c8331d;
  --blue: #2997ff;
  --blue-soft: #0a2f52;
  --success: #30d158;
  --success-bg: #0d2f18;
  --error: #ff6961;
  --error-bg: #381717;
  --focus: #64d2ff;
  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 16px;
  --space-xs: 0.5rem;
  --space-sm: 0.75rem;
  --space-md: 1rem;
  --space-lg: 1.5rem;
  --space-xl: 2rem;
  --space-2xl: 3rem;
  --space-3xl: 4.5rem;
  --ease-out: cubic-bezier(0.22, 1, 0.36, 1);
  --z-sticky: 20;
}

* {
  box-sizing: border-box;
}

[hidden] {
  display: none !important;
}

html {
  min-width: 320px;
  overflow-x: clip;
  background: var(--bg);
  color-scheme: dark;
  scroll-behavior: smooth;
}

html.lesson-flow-active {
  scroll-snap-type: y mandatory;
  overscroll-behavior-y: none;
}

body {
  min-height: 100vh;
  min-height: 100dvh;
  margin: 0;
  overflow-x: clip;
  background: var(--bg);
  color: var(--cream);
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", "Segoe UI", system-ui, sans-serif;
  font-size: 1rem;
  font-kerning: normal;
  line-height: 1.6;
  text-rendering: optimizeLegibility;
}

button,
input {
  font: inherit;
}

button,
a,
input[type="range"] {
  touch-action: manipulation;
}

button:focus-visible,
a:focus-visible,
input:focus-visible,
summary:focus-visible {
  outline: 3px solid var(--focus);
  outline-offset: 3px;
}

.lesson-hero[tabindex="-1"]:focus,
.lesson-section[tabindex="-1"]:focus,
.completion[tabindex="-1"]:focus {
  outline: none;
}

h2[tabindex="-1"]:focus {
  outline: none;
}

button:disabled {
  cursor: not-allowed;
  opacity: 0.48;
}

.skip-link {
  position: fixed;
  z-index: calc(var(--z-sticky) + 1);
  top: 0.75rem;
  left: 0.75rem;
  padding: 0.75rem 1rem;
  border-radius: var(--radius-sm);
  background: var(--cream);
  color: var(--bg);
  transform: translateY(-160%);
  transition: transform 180ms var(--ease-out);
}

.skip-link:focus {
  transform: translateY(0);
}

.lesson-nav {
  position: sticky;
  z-index: var(--z-sticky);
  top: 0;
  border-bottom: 1px solid var(--line);
  background: #0e121ef2;
  backdrop-filter: blur(12px);
}

.nav-main {
  display: grid;
  width: min(100% - 2rem, 70rem);
  min-height: 4rem;
  margin-inline: auto;
  grid-template-columns: auto minmax(0, 1fr);
  gap: var(--space-md);
  align-items: center;
}

.brand {
  color: var(--cream);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: 1rem;
  font-weight: 800;
  text-decoration: none;
}

.brand span {
  color: var(--orange);
}

.voice-controls {
  display: flex;
  gap: 0.25rem;
  align-items: center;
  justify-self: end;
}

.nav-button {
  min-height: 2.75rem;
  padding: 0.5rem 0.75rem;
  border: 0;
  border-radius: var(--radius-sm);
  background: transparent;
  color: var(--cream-muted);
  cursor: pointer;
  font-size: 0.8125rem;
  font-weight: 700;
  transition: background-color 150ms ease, color 150ms ease, transform 100ms ease;
}

.nav-button-icon {
  min-width: 2.75rem;
  padding-inline: 0;
  font-size: 1.25rem;
}

.nav-button:hover:not(:disabled) {
  background: var(--surface-raised);
  color: var(--cream);
}

.nav-button:active:not(:disabled) {
  transform: scale(0.96);
}

.progress-rail {
  height: 3px;
  overflow: hidden;
  background: var(--line);
}

.progress-rail span {
  display: block;
  width: 100%;
  height: 100%;
  background: var(--orange);
  transform: scaleX(0);
  transform-origin: left center;
  transition: transform 300ms var(--ease-out);
}

.audio-feedback {
  width: min(100% - 2rem, 70rem);
  margin: 0 auto;
  padding: 0.25rem 0 0.45rem;
}

.audio-status {
  min-height: 1.25rem;
  margin: 0;
  color: var(--cream-dim);
  font-size: 0.75rem;
  text-align: right;
}

.voice-progress {
  height: 2px;
  margin-top: 0.3rem;
  overflow: hidden;
  background: transparent;
}

.voice-progress span {
  display: block;
  width: 100%;
  height: 100%;
  background: var(--blue);
  opacity: 0;
  transform: scaleX(0);
  transform-origin: left center;
  transition: transform 120ms linear, opacity 150ms ease;
}

.voice-progress.is-active span {
  opacity: 0.72;
}

.lesson-hero,
.lesson-section {
  width: min(100% - 2rem, 70rem);
  margin-inline: auto;
}

.lesson-hero {
  display: grid;
  min-height: calc(100dvh - 5.6rem);
  grid-template-columns: minmax(0, 1.08fr) minmax(18rem, 0.92fr);
  gap: var(--space-3xl);
  align-items: center;
  padding-block: var(--space-3xl);
}

.hero-copy {
  max-width: 40rem;
}

.preview-label,
.step-index,
.equation-label {
  color: var(--cream-muted);
  font-size: 0.8125rem;
  font-weight: 700;
}

.preview-label {
  margin: 0 0 var(--space-md);
}

h1,
h2,
p {
  text-wrap: pretty;
}

h1,
h2 {
  text-wrap: balance;
}

h1 {
  max-width: 13ch;
  margin: 0;
  font-size: 4rem;
  line-height: 1.02;
  letter-spacing: -0.035em;
}

h2 {
  max-width: 18ch;
  margin: var(--space-sm) 0 0;
  font-size: 2.25rem;
  line-height: 1.12;
  letter-spacing: -0.025em;
}

.hero-lead {
  max-width: 58ch;
  margin: var(--space-lg) 0 0;
  color: var(--cream-muted);
  font-size: 1.125rem;
  line-height: 1.7;
}

.hero-actions,
.completion-actions {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-md);
  align-items: center;
  margin-top: var(--space-xl);
}

.primary-button,
.text-button,
.choice-button {
  min-height: 3rem;
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-weight: 750;
}

.primary-button {
  padding: 0.75rem 1.125rem;
  border: 1px solid var(--orange);
  background: var(--orange);
  color: #120b09;
  transition: background-color 150ms ease, border-color 150ms ease, transform 100ms ease;
}

.primary-button:hover:not(:disabled) {
  border-color: var(--orange-hover);
  background: var(--orange-hover);
}

.primary-button:active:not(:disabled) {
  border-color: var(--orange-pressed);
  background: var(--orange-pressed);
  transform: scale(0.98);
}

.text-button {
  padding: 0.75rem 0.25rem;
  border: 0;
  background: transparent;
  color: var(--cream);
  text-decoration: underline;
  text-decoration-color: var(--line-strong);
  text-underline-offset: 0.3em;
}

.text-button:hover {
  text-decoration-color: var(--cream);
}

.link-button {
  display: inline-grid;
  place-items: center;
}

.hero-note {
  max-width: 58ch;
  margin: var(--space-md) 0 0;
  color: var(--cream-dim);
  font-size: 0.875rem;
}

.hero-equation {
  position: relative;
  display: grid;
  min-height: 27rem;
  place-content: center;
  overflow: hidden;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius-lg);
  background: var(--surface);
  text-align: center;
}

.equation-label {
  margin-bottom: var(--space-lg);
}

.equation-main,
.final-answer,
.coordinate-formula,
.angle-equations,
.math-choice {
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
}

.equation-main {
  font-size: 3rem;
  font-weight: 800;
  letter-spacing: -0.04em;
}

.equation-interval {
  margin-top: var(--space-sm);
  color: var(--cream-muted);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: 1rem;
}

.causal-preview {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.75rem;
  margin-top: var(--space-2xl);
}

.preview-dot {
  width: 0.75rem;
  height: 0.75rem;
  border: 2px solid var(--blue);
  border-radius: 50%;
  background: var(--surface);
}

.preview-line {
  width: 5rem;
  height: 2px;
  background: var(--line-strong);
}

.preview-answer {
  display: grid;
  width: 2.25rem;
  height: 2.25rem;
  place-items: center;
  border: 1px solid var(--line-strong);
  border-radius: 50%;
  color: var(--cream-muted);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
}

.lesson-section {
  position: relative;
  min-height: 44rem;
  padding-block: var(--space-3xl);
  border-top: 1px solid var(--line);
  scroll-margin-top: 6.5rem;
}

.section-toolbar {
  display: flex;
  align-items: center;
  justify-content: flex-end;
  gap: 0.75rem;
  margin-bottom: var(--space-lg);
}

.section-toolbar > span {
  color: var(--cream-dim);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: 0.75rem;
  font-weight: 800;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.section-replay {
  min-height: 2.75rem;
  padding: 0.55rem 0.9rem;
  border: 1px solid var(--line-strong);
  border-radius: 999px;
  background: var(--surface-raised);
  color: var(--cream);
  cursor: pointer;
  font-size: 0.875rem;
  font-weight: 750;
  transition: border-color 140ms ease, background 140ms ease, color 140ms ease, transform 140ms ease;
}

.section-replay:not(:disabled):hover,
.section-replay:not(:disabled):focus-visible {
  border-color: var(--blue);
  background: var(--blue-soft);
  color: var(--blue);
  transform: translateY(-1px);
}

.lesson-section.is-opening .step-grid,
.lesson-section.is-opening .transfer-inner {
  animation: section-open 520ms var(--ease-out) both;
}

@keyframes section-open {
  from {
    opacity: 0.4;
    clip-path: inset(0 0 12% 0);
    transform: translateY(1rem);
  }
  to {
    opacity: 1;
    clip-path: inset(0 0 0 0);
    transform: translateY(0);
  }
}

.step-grid {
  display: grid;
  grid-template-columns: minmax(17rem, 0.82fr) minmax(20rem, 1.18fr);
  gap: var(--space-3xl);
  align-items: center;
}

.step-grid.visual-first {
  grid-template-columns: minmax(20rem, 1.18fr) minmax(17rem, 0.82fr);
}

.step-copy {
  max-width: 38rem;
}

.step-copy > p {
  max-width: 60ch;
  margin: var(--space-lg) 0 0;
  color: var(--cream-muted);
  font-size: 1.0625rem;
}

.step-copy strong {
  color: var(--cream);
}

.coordinate-formula {
  width: fit-content;
  margin-top: var(--space-lg);
  padding: 0.75rem 1rem;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius-sm);
  background: var(--surface);
  font-size: 1.35rem;
}

.coordinate-formula strong {
  color: var(--blue);
}

.coordinate-formula span {
  color: var(--cream-muted);
}

.question-copy {
  color: var(--cream) !important;
}

.choice-row,
.choice-grid,
.transfer-choices {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-sm);
  margin-top: var(--space-lg);
}

.choice-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
}

.transfer-choices {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.choice-button {
  min-width: 8rem;
  padding: 0.75rem 1rem;
  border: 1px solid var(--line-strong);
  background: var(--surface);
  color: var(--cream);
  transition: border-color 150ms ease, background-color 150ms ease, transform 100ms ease;
}

.choice-button:hover:not(:disabled) {
  border-color: var(--blue);
  background: var(--surface-raised);
}

.choice-button:active:not(:disabled) {
  transform: scale(0.98);
}

.choice-button.is-correct {
  border-color: var(--success);
  background: var(--success-bg);
  color: var(--success);
}

.choice-button.is-wrong {
  border-color: var(--error);
  background: var(--error-bg);
  color: var(--error);
}

.local-feedback {
  min-height: 3.3rem;
  margin-top: var(--space-md) !important;
  padding: 0.75rem 0;
  color: var(--cream-dim) !important;
  font-size: 0.9375rem !important;
}

.local-feedback.success {
  color: var(--success) !important;
}

.local-feedback.error {
  color: var(--error) !important;
}

.revealed-explanation {
  margin-top: var(--space-lg);
  padding-top: var(--space-lg);
  border-top: 1px solid var(--line);
}

.revealed-explanation p {
  margin: 0;
  color: var(--cream-muted);
}

.next-button {
  margin-top: var(--space-lg);
}

.transcript {
  margin-top: var(--space-xl);
  color: var(--cream-muted);
  font-size: 0.875rem;
}

.transcript summary {
  width: fit-content;
  min-height: 2.75rem;
  padding-block: 0.65rem;
  color: var(--cream-dim);
  cursor: pointer;
  font-weight: 650;
}

.transcript[open] summary {
  color: var(--cream);
}

.transcript p {
  max-width: 62ch;
  margin: var(--space-sm) 0 0;
  color: var(--cream-muted);
}

.visual-stage {
  position: relative;
  min-width: 0;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: var(--radius-lg);
  background: var(--surface);
}

.coordinate-stage {
  display: grid;
  min-height: 31rem;
  place-items: center;
}

.axis-card {
  position: relative;
  width: min(80%, 25rem);
  aspect-ratio: 1;
}

.axis-line {
  position: absolute;
  background: var(--line-strong);
}

.axis-x {
  top: 50%;
  right: 0;
  left: 0;
  height: 1px;
}

.axis-y {
  top: 0;
  bottom: 0;
  left: 50%;
  width: 1px;
}

.axis-name {
  position: absolute;
  color: var(--cream-dim);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: 0.875rem;
}

.axis-name-x {
  top: calc(50% + 0.75rem);
  right: 0;
  color: var(--blue);
}

.axis-name-y {
  top: 0;
  left: calc(50% + 0.75rem);
}

.coordinate-point {
  position: absolute;
  top: 23%;
  left: 25%;
  width: 1rem;
  height: 1rem;
  border: 3px solid var(--cream);
  border-radius: 50%;
  background: var(--surface);
  transform: translate(-50%, -50%);
}

.coordinate-drop {
  position: absolute;
  top: 23%;
  bottom: 50%;
  left: 25%;
  width: 2px;
  background: var(--blue);
  transform: translateX(-50%);
}

.coordinate-value {
  position: absolute;
  top: calc(50% + 0.6rem);
  left: 25%;
  color: var(--blue);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  transform: translateX(-50%);
}

.circle-stage {
  padding: var(--space-lg);
}

.unit-circle,
.angle-stage svg {
  display: block;
  width: 100%;
  max-width: 32rem;
  margin-inline: auto;
}

.circle-axis {
  stroke: var(--line-strong);
  stroke-width: 1.5;
}

.circle-outline {
  fill: none;
  stroke: var(--cream-muted);
  stroke-width: 3;
}

.scan-line,
.fixed-line {
  stroke: var(--blue);
  stroke-width: 3;
}

.intersection-point {
  fill: var(--cream);
  stroke: var(--bg);
  stroke-width: 3;
}

.lesson-section.is-current:not(.is-cue-driven) .scan-line {
  animation: scan-in 700ms var(--ease-out) both;
}

.lesson-section.is-current:not(.is-cue-driven) .intersection-point {
  animation: point-in 420ms 480ms var(--ease-out) both;
}

@keyframes scan-in {
  from {
    opacity: 0;
    transform: translateX(4.5rem);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

@keyframes point-in {
  from {
    opacity: 0;
    transform: scale(0.45);
  }
  to {
    opacity: 1;
    transform: scale(1);
  }
}

.axis-text,
.line-value,
.angle-label,
.reference-label {
  fill: var(--cream-muted);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: 0.875rem;
  paint-order: stroke fill;
  stroke: var(--surface);
  stroke-linejoin: round;
  stroke-width: 5px;
}

.line-value {
  fill: var(--blue);
  text-anchor: middle;
}

.variation-control {
  display: grid;
  gap: var(--space-sm);
  padding: var(--space-lg);
  border-top: 1px solid var(--line);
  background: var(--surface-raised);
}

.variation-heading {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: var(--space-sm);
  color: var(--cream-muted);
  font-size: 0.875rem;
}

.variation-heading strong,
.variation-heading span {
  color: var(--cream);
}

.variation-control input {
  width: 100%;
  min-height: 2.75rem;
  accent-color: var(--blue);
  cursor: ew-resize;
}

.variation-control p {
  margin: 0;
  color: var(--cream-dim);
  font-size: 0.8125rem;
}

.reason-chain,
.completion-chain {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  align-items: center;
  margin-top: var(--space-lg);
  color: var(--cream-muted);
  font-size: 0.875rem;
}

.reason-chain span:nth-child(odd),
.completion-chain span:nth-child(odd) {
  padding: 0.4rem 0.65rem;
  border: 1px solid var(--line-strong);
  border-radius: 999px;
  background: var(--surface);
  color: var(--cream);
}

.angle-stage {
  display: grid;
  min-height: 34rem;
  place-items: center;
  padding: var(--space-lg);
}

.radius-line {
  stroke: var(--cream-muted);
  stroke-width: 2;
}

.reference-arc {
  fill: none;
  stroke: var(--blue);
  stroke-width: 3;
}

.angle-distance-guide {
  stroke: var(--orange);
  stroke-width: 2;
  stroke-dasharray: 7 6;
}

.angle-distance-label,
.angle-question-mark {
  fill: var(--orange);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: 0.9rem;
  font-weight: 800;
  paint-order: stroke fill;
  stroke: var(--surface);
  stroke-linejoin: round;
  stroke-width: 5px;
  text-anchor: middle;
}

.angle-question-radius {
  stroke: var(--cream-muted);
  stroke-width: 2;
  stroke-dasharray: 8 7;
}

.angle-question-arc {
  fill: none;
  stroke: var(--orange);
  stroke-width: 4;
}

.angle-question-mark {
  font-size: 1.1rem;
}

.angle-stage.angle-resolved .angle-question-radius,
.angle-stage.angle-resolved .angle-question-arc,
.angle-stage.angle-resolved .angle-question-mark {
  opacity: 0 !important;
}

.angle-label {
  fill: var(--cream);
  font-size: 1.05rem;
  font-weight: 700;
}

.reference-label {
  fill: var(--blue);
  font-weight: 700;
}

.angle-equations {
  display: grid;
  gap: var(--space-sm);
  font-size: 1.05rem;
}

.angle-equations span {
  color: var(--cream-muted);
}

.solution-stage {
  display: grid;
  min-height: 36rem;
  place-items: center;
  padding: var(--space-xl);
}

.solution-circle {
  position: relative;
  width: min(100%, 29rem);
  aspect-ratio: 1;
}

.solution-ring {
  position: absolute;
  inset: 13%;
  border: 3px solid var(--cream-muted);
  border-radius: 50%;
}

.solution-axis,
.solution-fixed-line {
  position: absolute;
  background: var(--line-strong);
}

.solution-axis-x {
  top: 50%;
  right: 4%;
  left: 4%;
  height: 1px;
}

.solution-axis-y {
  top: 4%;
  bottom: 4%;
  left: 50%;
  width: 1px;
}

.solution-fixed-line {
  top: 9%;
  bottom: 9%;
  left: 31.5%;
  width: 3px;
  background: var(--blue);
}

.solution-point {
  position: absolute;
  width: 2.75rem;
  height: 2.75rem;
  padding: 0;
  border: 3px solid var(--cream);
  border-radius: 50%;
  background: var(--surface);
  cursor: pointer;
  transform: translate(-50%, -50%);
  transition: background-color 150ms ease, border-color 150ms ease, transform 100ms ease;
}

.solution-point::after {
  position: absolute;
  inset: 0.65rem;
  border-radius: 50%;
  background: var(--cream);
  content: "";
}

.solution-point:hover:not(:disabled) {
  border-color: var(--blue);
  transform: translate(-50%, -50%) scale(1.06);
}

.solution-point:active:not(:disabled) {
  transform: translate(-50%, -50%) scale(0.96);
}

.solution-point.is-selected {
  border-color: var(--success);
  background: var(--success-bg);
}

.solution-point.is-selected::after {
  background: var(--success);
}

.solution-point.is-selected:disabled,
.choice-button.is-correct:disabled {
  opacity: 1;
}

.narration-cue {
  position: absolute;
  z-index: 4;
  top: 1rem;
  left: 1rem;
  display: flex;
  max-width: min(28rem, calc(100% - 2rem));
  min-height: 2.75rem;
  align-items: center;
  gap: 0.65rem;
  padding: 0.55rem 0.75rem;
  border: 1px solid #79d5ff55;
  border-radius: var(--radius-sm);
  background: #0e121ee8;
  box-shadow: 0 0.75rem 2.5rem #070a1166;
  color: var(--cream);
  font-size: 0.8125rem;
  font-weight: 700;
  line-height: 1.35;
  opacity: 0;
  pointer-events: none;
  transform: translateY(-0.35rem);
  transition: opacity 180ms ease, transform 220ms var(--ease-out);
}

.narration-cue.is-visible {
  opacity: 1;
  transform: translateY(0);
}

.narration-cue-dot {
  width: 0.55rem;
  height: 0.55rem;
  flex: 0 0 auto;
  border-radius: 50%;
  background: var(--blue);
  box-shadow: 0 0 0 0.3rem #79d5ff22;
}

.transfer-copy > .narration-cue {
  position: relative;
  top: auto;
  left: auto;
  width: fit-content;
  margin: var(--space-lg) auto 0;
}

.cue-target {
  transition: opacity 260ms ease, filter 260ms ease;
}

/* These objects are rendered at the media clock's exact time, including seek
   and pause. A wall-clock CSS transition/keyframe would create a second owner
   and make the same timestamp depend on the path taken to reach it. Buttons
   outside the marked teaching surfaces retain their normal UI feedback. */
.melo-clock-owned,
.melo-clock-owned *,
.melo-clock-owned::before,
.melo-clock-owned::after,
.melo-clock-owned *::before,
.melo-clock-owned *::after {
  animation: none !important;
  transition: none !important;
}

.cue-target.is-cue-hidden {
  opacity: 0 !important;
  pointer-events: none !important;
}

.cue-target.is-cue-revealing {
  animation: cue-reveal 460ms var(--ease-out) both;
}

.is-cue-focused {
  filter: drop-shadow(0 0 0.6rem #79d5ffaa) brightness(1.18);
}

.coordinate-formula.is-cue-focused,
.reason-chain.is-cue-focused,
.final-answer.is-cue-focused,
.transfer-copy > p.is-cue-focused {
  outline: 2px solid #79d5ff88;
  outline-offset: 0.45rem;
  border-radius: var(--radius-sm);
}

.visual-stage.is-narrating {
  border-color: #79d5ff66;
}

.visual-stage.has-narration-cue {
  padding-top: 5rem;
  scroll-margin-top: 6.75rem;
}

@keyframes cue-reveal {
  from {
    opacity: 0;
    filter: blur(4px);
  }
  to {
    opacity: 1;
    filter: blur(0);
  }
}

.solution-point.is-wrong {
  border-color: var(--error);
  background: var(--error-bg);
}

.point-60 {
  top: 18.8%;
  left: 68.5%;
}

.point-120 {
  top: 18.8%;
  left: 31.5%;
}

.point-240 {
  top: 81.2%;
  left: 31.5%;
}

.point-300 {
  top: 81.2%;
  left: 68.5%;
}

.solution-label {
  position: absolute;
  color: var(--success);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: 0.875rem;
  font-weight: 800;
}

.label-120 {
  top: 7%;
  left: 16%;
}

.label-240 {
  bottom: 5%;
  left: 15%;
}

.final-answer {
  width: fit-content;
  padding: 0.75rem 1rem;
  border: 1px solid var(--success);
  border-radius: var(--radius-sm);
  background: var(--success-bg);
  color: var(--success);
  font-size: 1.25rem;
  font-weight: 800;
}

.transfer-section {
  min-height: 100dvh;
}

.transfer-inner {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: var(--space-3xl);
}

.transfer-copy {
  max-width: 48rem;
  margin-inline: auto;
  text-align: center;
}

.transfer-copy h2 {
  margin-inline: auto;
}

.transfer-copy > p {
  margin-inline: auto;
}

.transfer-choices {
  max-width: 38rem;
  margin-inline: auto;
}

.completion {
  grid-column: 1 / -1;
  max-width: 52rem;
  margin-inline: auto;
  padding: var(--space-2xl);
  border: 1px solid var(--line-strong);
  border-radius: var(--radius-lg);
  background: var(--surface);
  text-align: center;
}

.completion-mark {
  display: grid;
  width: 3.5rem;
  height: 3.5rem;
  margin: 0 auto var(--space-lg);
  place-items: center;
  border: 1px solid var(--success);
  border-radius: 50%;
  background: var(--success-bg);
  color: var(--success);
  font-size: 1.5rem;
  font-weight: 800;
}

.completion h2 {
  max-width: 20ch;
  margin-inline: auto;
}

.completion > p:not(.completion-mark) {
  max-width: 60ch;
  margin: var(--space-lg) auto 0;
  color: var(--cream-muted);
}

.completion-chain,
.completion-actions {
  justify-content: center;
}

.noscript {
  margin: 2rem;
  padding: 1rem;
  border: 1px solid var(--error);
  border-radius: var(--radius-sm);
  background: var(--error-bg);
  color: var(--error);
}

@media (max-width: 840px) {
  .lesson-hero,
  .step-grid,
  .step-grid.visual-first {
    grid-template-columns: 1fr;
  }

  .lesson-hero {
    gap: var(--space-2xl);
  }

  .hero-equation {
    min-height: 22rem;
  }

  .step-grid .visual-stage,
  .step-grid.visual-first .visual-stage {
    order: 1;
  }

  .step-grid .step-copy,
  .step-grid.visual-first .step-copy {
    order: 2;
  }

  .lesson-section {
    min-height: auto;
  }
}

@media (max-width: 600px) {
  .nav-main {
    width: min(100% - 1.25rem, 70rem);
    grid-template-columns: auto minmax(0, 1fr) auto;
    gap: 0.5rem;
  }

  .voice-controls {
    gap: 0;
  }

  .nav-button {
    padding-inline: 0.5rem;
  }

  .audio-feedback {
    width: min(100% - 1.25rem, 70rem);
  }

  .lesson-hero,
  .lesson-section {
    width: min(100% - 1.25rem, 70rem);
  }

  .lesson-hero {
    min-height: auto;
    padding-block: var(--space-2xl);
  }

  h1 {
    font-size: 2.75rem;
  }

  h2 {
    font-size: 1.75rem;
  }

  .hero-lead,
  .step-copy > p {
    font-size: 1rem;
  }

  .hero-actions,
  .completion-actions {
    align-items: stretch;
    flex-direction: column;
  }

  .hero-actions .primary-button,
  .hero-actions .text-button,
  .completion-actions .primary-button,
  .completion-actions .text-button {
    width: 100%;
  }

  .hero-equation {
    min-height: 19rem;
  }

  .equation-main {
    font-size: 2.25rem;
  }

  .lesson-section {
    padding-block: var(--space-2xl);
    scroll-margin-top: 6rem;
  }

  .step-grid,
  .step-grid.visual-first {
    gap: var(--space-2xl);
  }

  .choice-grid,
  .transfer-choices {
    grid-template-columns: 1fr;
  }

  .choice-row .choice-button,
  .choice-grid .choice-button,
  .transfer-choices .choice-button {
    width: 100%;
  }

  .coordinate-stage,
  .angle-stage,
  .solution-stage {
    min-height: 24rem;
  }

  .circle-stage,
  .angle-stage,
  .solution-stage {
    padding: var(--space-sm);
  }

  .solution-point {
    width: 2.75rem;
    height: 2.75rem;
  }

  .reason-chain,
  .completion-chain {
    justify-content: center;
  }

  .completion {
    padding: var(--space-xl) var(--space-lg);
  }
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }

  *,
  *::before,
  *::after {
    animation-iteration-count: 1 !important;
  }
}

/* Transfer proof ladder: three different retrieval demands, one stable visual tool. */
.skill-proof-progress {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0;
  margin: 0 0 1rem;
  border-bottom: 1px solid var(--apple-separator);
}

.skill-proof-progress > span {
  position: relative;
  display: grid;
  min-width: 0;
  grid-template-columns: 1.35rem minmax(0, 1fr);
  gap: 0.35rem;
  align-items: center;
  padding: 0 0.35rem 0.7rem;
  color: var(--apple-tertiary);
}

.skill-proof-progress > span::after {
  position: absolute;
  right: 0;
  bottom: -1px;
  left: 0;
  height: 2px;
  border-radius: 2px;
  background: transparent;
  content: "";
  transition: background-color 220ms ease;
}

.skill-proof-progress b {
  display: grid;
  width: 1.3rem;
  height: 1.3rem;
  place-items: center;
  border: 1px solid var(--apple-separator);
  border-radius: 50%;
  color: inherit;
  font-size: 0.68rem;
  line-height: 1;
}

.skill-proof-progress small {
  min-width: 0;
  overflow: hidden;
  font-size: 0.68rem;
  line-height: 1.2;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.skill-proof-progress > .is-current {
  color: var(--apple-label);
}

.skill-proof-progress > .is-current::after {
  background: var(--apple-blue);
}

.skill-proof-progress > .is-complete {
  color: var(--apple-green);
}

.transfer-round-kicker {
  margin: 0 0 0.35rem !important;
  color: var(--apple-secondary) !important;
  font-size: 0.78rem;
  font-weight: 600;
}

.transfer-equation-choices {
  display: grid;
  grid-template-columns: 1fr;
  gap: 0.55rem;
}

.transfer-equation-choices[hidden] {
  display: none;
}

.transfer-equation-choices .choice-button {
  justify-content: flex-start;
  padding-inline: 1rem;
  text-align: left;
}

.transfer-round-resolution {
  display: grid;
  gap: 0.75rem;
  padding-top: 0.85rem;
  border-top: 1px solid var(--apple-separator);
}

.transfer-round-resolution[hidden] {
  display: none;
}

.transfer-why {
  border-radius: 12px;
  background: var(--apple-surface);
  box-shadow: inset 0 0 0 1px #ffffff0d;
}

.transfer-why summary {
  display: flex;
  min-height: 2.75rem;
  align-items: center;
  justify-content: space-between;
  padding: 0.65rem 0.85rem;
  color: var(--apple-label);
  cursor: pointer;
  font-size: 0.9rem;
  font-weight: 600;
  list-style: none;
}

.transfer-why summary::-webkit-details-marker {
  display: none;
}

.transfer-why summary::after {
  color: var(--apple-secondary);
  content: "+";
  font-size: 1.1rem;
  font-weight: 400;
}

.transfer-why[open] summary::after {
  content: "−";
}

.transfer-why p {
  margin: 0;
  padding: 0 0.85rem 0.85rem;
  color: var(--apple-secondary);
  font-size: 0.88rem;
  line-height: 1.5;
}

#transfer-round-next {
  justify-self: start;
}

#step-5 .transfer-stage[data-transfer-round="reverse-reading"] .transfer-line {
  stroke: var(--apple-blue);
}

#step-5 .transfer-stage[data-transfer-round="reference-angle-transfer"] .transfer-line,
#step-5 .transfer-stage[data-transfer-round="reference-angle-transfer"] .transfer-line-candidate-horizontal,
#step-5 .transfer-stage[data-transfer-round="shortcut-breaker"] .transfer-line,
#step-5 .transfer-stage[data-transfer-round="shortcut-breaker"] .transfer-line-candidate-horizontal {
  stroke: var(--apple-orange);
}

@media (max-width: 720px) {
  .skill-proof-progress small {
    white-space: normal;
  }

  .skill-proof-progress > span {
    grid-template-columns: 1fr;
    align-content: start;
  }

  #step-5 .transfer-stage {
    min-height: 28rem;
    padding-top: 6.6rem;
  }

  #step-5 .transfer-stage > #transfer-circle-map {
    transform: translateY(1.45rem) scale(0.69);
  }

  .transfer-brief {
    width: calc(100% - 1.25rem);
    min-width: 0;
  }

  .transfer-angle-grid {
    grid-template-columns: repeat(4, minmax(0, 1fr));
  }
}

/* Step 5 memory tool: one first-quadrant object carries the entire
   explanation. Values transform in place and then travel to the reversed
   sine order; no caption card or secondary table covers the geometry. */
.angle-memory-stage {
  --memory-quadrant: var(--melo-memory-quadrant, 0);
  --memory-angles: var(--melo-memory-angles, 0);
  --memory-counts: var(--melo-memory-counts, 0);
  --memory-root: var(--melo-memory-root, 0);
  --memory-divide: var(--melo-memory-divide, 0);
  --memory-template: var(--melo-memory-template, 0);
  --memory-simplify: var(--melo-memory-simplify, 0);
  --memory-sweep: var(--melo-memory-sweep, 0);
  --memory-reverse: var(--melo-memory-reverse, 0);
  --memory-focus: var(--melo-memory-focus, 0);
  --memory-foundation-origin: var(--melo-memory-foundation-origin, 0);
  --memory-foundation-circle: var(--melo-memory-foundation-circle, 0);
  --memory-foundation-units: var(--melo-memory-foundation-units, 0);
  --memory-foundation-turn: var(--melo-memory-foundation-turn, 0);
  --memory-foundation-repeat: var(--melo-memory-foundation-repeat, 0);
  --memory-foundation-exit: var(--melo-memory-foundation-exit, 0);
  position: absolute;
  z-index: 14;
  inset: 0;
  overflow: hidden;
  border-radius: inherit;
  background: #000;
  transition: opacity 260ms ease, visibility 0s linear 0s;
}

.transfer-stage.is-memory-mode > :not(.angle-memory-stage) {
  visibility: hidden;
  opacity: 0;
  pointer-events: none;
}

.transfer-stage:not(.is-memory-mode) .angle-memory-stage {
  visibility: hidden;
  opacity: 0;
  pointer-events: none;
  transition: opacity 260ms ease, visibility 0s linear 260ms;
}

.memory-quadrant {
  position: absolute;
  z-index: 2;
  top: 3.2rem;
  left: 50%;
  width: min(100%, 28rem);
  aspect-ratio: 1;
  opacity: var(--memory-quadrant);
  transform: translateX(-50%) translateY(calc((1 - var(--memory-quadrant)) * 0.8rem)) scale(calc(0.97 + var(--memory-quadrant) * 0.03));
}

.memory-quadrant svg {
  display: block;
  width: 100%;
  height: 100%;
  overflow: visible;
}

.memory-axis,
.memory-quarter-arc,
.memory-rays line {
  fill: none;
  vector-effect: non-scaling-stroke;
}

.memory-axis {
  stroke: #ffffff36;
  stroke-width: 1.8;
}

.memory-foundation-origin,
.memory-foundation-units,
.memory-foundation-cardinals,
.memory-repeat-proof {
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", "Segoe UI", system-ui, sans-serif;
  font-variant-numeric: tabular-nums;
  transition: opacity 240ms ease, filter 280ms ease;
}

.memory-foundation-origin {
  fill: #f5f5f7;
  opacity: calc(var(--memory-foundation-origin) * (1 - var(--memory-foundation-exit)));
}

.memory-foundation-origin text,
.memory-foundation-units text,
.memory-foundation-cardinals text {
  fill: #aeaeb2;
  font-size: 12px;
  font-weight: 680;
}

.memory-foundation-units {
  fill: var(--apple-blue, #2997ff);
  opacity: calc(var(--memory-foundation-units) * (1 - var(--memory-foundation-exit)));
}

.memory-foundation-cardinals {
  opacity: calc(var(--memory-foundation-turn) * (1 - var(--memory-foundation-exit)));
}

.memory-foundation-cardinals text { fill: #f5f5f7; }

.memory-turn-track,
.memory-turn-progress {
  fill: none;
  vector-effect: non-scaling-stroke;
}

.memory-turn-track {
  stroke: #ffffff12;
  stroke-width: 7;
  opacity: calc(var(--memory-foundation-turn) * (1 - var(--memory-foundation-exit)));
}

.memory-turn-progress {
  stroke: var(--apple-orange, #ff9f0a);
  stroke-width: 4;
  stroke-linecap: round;
  stroke-dasharray: 1;
  stroke-dashoffset: 1;
  opacity: calc(var(--memory-foundation-turn) * (1 - var(--memory-foundation-exit)));
  transform: rotate(-90deg);
  transform-box: fill-box;
  transform-origin: center;
}

.memory-turn-point {
  fill: var(--apple-orange, #ff9f0a);
  opacity: calc(var(--memory-foundation-turn) * (1 - var(--memory-foundation-exit)));
  filter: drop-shadow(0 0 8px #ff9f0a88);
}

.memory-repeat-proof {
  opacity: calc(var(--memory-foundation-repeat) * (1 - var(--memory-foundation-exit)));
}

.memory-repeat-proof text {
  fill: #f5f5f7;
  font-size: 14px;
  font-weight: 720;
}

.memory-repeat-proof .memory-repeat-rule {
  fill: var(--apple-orange, #ff9f0a);
  font-size: 12px;
}

.memory-quarter-arc {
  stroke: #f5f5f7;
  stroke-width: 3;
  stroke-dasharray: 1;
  stroke-dashoffset: calc(1 - var(--memory-foundation-circle));
  stroke-linecap: round;
}

.memory-rays line {
  stroke: #ffffff20;
  stroke-width: 1.5;
  stroke-dasharray: 1;
  stroke-dashoffset: calc(1 - var(--memory-angles));
}

.memory-projection-guides line {
  fill: none;
  stroke-width: 3;
  opacity: var(--memory-sweep);
  vector-effect: non-scaling-stroke;
}

.memory-projection-cos { stroke: var(--apple-blue, #2997ff); }
.memory-projection-sin { stroke: var(--apple-orange, #ff9f0a); }

.memory-sweep-point {
  fill: #f5f5f7;
  opacity: var(--memory-sweep);
  filter: drop-shadow(0 0 7px #ffffff66);
}

.memory-axis-caption {
  fill: #8e8e93;
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", "Segoe UI", system-ui, sans-serif;
  font-size: 12px;
  font-weight: 650;
  opacity: var(--memory-sweep);
}

.memory-coordinate-pair {
  position: absolute;
  z-index: 8;
  bottom: 0.4rem;
  left: 0.6rem;
  color: #f5f5f7;
  font-size: clamp(0.82rem, 3.2cqw, 0.98rem);
  opacity: var(--memory-sweep);
  pointer-events: none;
  text-shadow: 0 2px 10px #000;
  transform: translateY(calc((1 - var(--memory-sweep)) * 0.35rem));
  transition: opacity 220ms ease, transform 420ms var(--melo-morph, cubic-bezier(.22, 1, .36, 1));
}

.memory-angle-label {
  position: absolute;
  z-index: 5;
  display: grid;
  justify-items: center;
  gap: 0.02rem;
  color: #f5f5f7;
  font-variant-numeric: tabular-nums;
  opacity: var(--memory-angles);
  text-shadow: 0 2px 8px #000;
  transform: translate(-50%, -50%) translateY(calc((1 - var(--memory-angles)) * 0.45rem));
}

.memory-angle-label b {
  font-size: clamp(0.72rem, 2.8cqw, 0.86rem);
  font-weight: 720;
}

.memory-angle-label small {
  color: #8e8e93;
  font-size: clamp(0.58rem, 2.1cqw, 0.68rem);
}

.memory-angle-label-0 { top: 88%; left: 88%; }
.memory-angle-label-30 { top: 61%; left: 80%; }
.memory-angle-label-45 { top: 42%; left: 61%; }
.memory-angle-label-60 { top: 28%; left: 47%; }
/* Keep the endpoint label outside the sweep point and its glow. The point
   stays on the y-axis; only its degree/radian annotation moves to the left. */
.memory-angle-label-90 { top: 20%; left: 5%; }

.memory-value-token {
  position: absolute;
  z-index: 7;
  display: grid;
  width: 4.5rem;
  min-height: 2.8rem;
  place-items: center;
  color: #f5f5f7;
  font-size: clamp(1.05rem, 4.7cqw, 1.35rem);
  font-variant-numeric: tabular-nums;
  opacity: var(--memory-counts);
  text-align: center;
  text-shadow: 0 3px 12px #000, 0 0 18px #2997ff22;
  transform: translate(-50%, -50%) scale(calc(0.88 + var(--memory-counts) * 0.12));
  transform-origin: center;
  will-change: left, top, transform, opacity;
}

.memory-value-token > span {
  grid-area: 1 / 1;
  white-space: nowrap;
}

.memory-token-builder {
  position: relative;
  display: block;
  width: 3.5rem;
  height: 3.2rem;
  filter: blur(calc(var(--memory-simplify) * 2px));
  opacity: calc(1 - var(--memory-simplify));
  transform: scale(calc(1 - var(--memory-simplify) * 0.05));
}

.memory-token-number,
.memory-token-radical,
.memory-token-denominator,
.memory-token-bar {
  position: absolute;
  left: 50%;
  font-family: "KaTeX_Main", "Times New Roman", serif;
}

.memory-token-number {
  top: calc(50% - var(--memory-divide) * 0.62rem);
  transform: translate(calc(-50% + var(--memory-root) * 0.32rem), -50%);
}

.memory-token-radical {
  top: calc(50% - var(--memory-divide) * 0.62rem);
  left: calc(50% - 0.42rem);
  overflow: hidden;
  font-size: 1.18em;
  line-height: 1;
  opacity: var(--memory-root);
  clip-path: inset(0 calc((1 - var(--memory-root)) * 100%) 0 0);
  transform: translate(-50%, -50%);
}

.memory-token-bar {
  top: calc(50% + 0.05rem);
  width: calc(var(--memory-divide) * 2rem);
  height: 1px;
  background: currentColor;
  opacity: var(--memory-divide);
  transform: translateX(-50%);
}

.memory-token-denominator {
  top: calc(50% + 0.72rem);
  font-size: 0.78em;
  opacity: var(--memory-divide);
  transform: translate(-50%, calc((1 - var(--memory-divide)) * -0.25rem));
}

.memory-token-final {
  filter: blur(calc((1 - var(--memory-simplify)) * 2px));
  opacity: var(--memory-simplify);
  transform: scale(calc(0.95 + var(--memory-simplify) * 0.05));
}

.memory-general-template {
  position: absolute;
  z-index: 8;
  top: 62%;
  left: 52%;
  display: grid;
  min-width: 7.5rem;
  place-items: center;
  gap: 0.1rem;
  color: #f5f5f7;
  opacity: var(--memory-template);
  text-align: center;
  text-shadow: 0 3px 14px #000, 0 0 20px #2997ff33;
  transform: translate(-50%, calc(-50% + (1 - var(--memory-template)) * 0.8rem)) scale(calc(0.9 + var(--memory-template) * 0.1));
  filter: blur(calc((1 - var(--memory-template)) * 2px));
  pointer-events: none;
  will-change: opacity, filter, transform;
}

.memory-general-template small,
.memory-general-template > span {
  color: #8e8e93;
  font-size: clamp(0.58rem, 2.1cqw, 0.7rem);
  font-style: normal;
  font-weight: 650;
  letter-spacing: 0.02em;
}

.memory-general-template strong {
  color: var(--apple-orange, #ff9f0a);
  font-size: clamp(1.45rem, 6.3cqw, 1.9rem);
  font-weight: 650;
  line-height: 1.1;
}

.memory-general-template i {
  color: var(--apple-orange, #ff9f0a);
  font-family: "KaTeX_Math", "Times New Roman", serif;
  font-style: italic;
}

.memory-value-token[data-pattern-slot="0"] { top: 77%; left: 91%; }
.memory-value-token[data-pattern-slot="1"] { top: 47%; left: 83%; }
.memory-value-token[data-pattern-slot="2"] { top: 24%; left: 67%; }
.memory-value-token[data-pattern-slot="3"] { top: 9%; left: 46%; }
.memory-value-token[data-pattern-slot="4"] { top: 4%; left: 17%; }

.memory-function-switch {
  position: absolute;
  z-index: 9;
  top: 0.95rem;
  right: 1rem;
  display: grid;
  min-width: 4.4rem;
  color: #f5f5f7;
  opacity: max(var(--memory-counts), var(--memory-sweep));
  text-align: right;
  pointer-events: none;
  transition: opacity 220ms ease;
}

.memory-function {
  display: inline-flex;
  grid-area: 1 / 1;
  flex-direction: column;
  align-items: flex-end;
  justify-content: flex-end;
  gap: 0.08rem;
  line-height: 1.05;
  transform: translateY(0);
}

.memory-function b { font-size: 1.2rem; }
.memory-function small { color: #8e8e93; }
.memory-function-cos { color: var(--apple-blue, #2997ff); opacity: clamp(0, calc(1 - var(--memory-reverse) * 2.05), 1); }
.memory-function-sin { color: var(--apple-orange, #ff9f0a); opacity: clamp(0, calc(var(--memory-reverse) * 2.05 - 1.05), 1); }

.angle-memory-stage[data-memory-check-function="sin"] [data-pattern-slot="1"],
.angle-memory-stage[data-memory-check-function="cos"] [data-pattern-slot="3"] {
  color: var(--apple-orange, #ff9f0a);
  text-shadow: 0 0 18px #ff9f0a8c;
}

.angle-memory-copy,
.transfer-round-copy {
  min-width: 0;
  width: 100%;
}

.angle-memory-copy > h2,
.transfer-round-copy > h2 {
  margin-top: 0.35rem;
}

.angle-memory-check {
  display: grid;
  gap: 0.7rem;
  margin-top: 0.9rem;
}

.memory-check-step {
  display: grid;
  gap: 0.65rem;
}

.memory-check-step > p {
  margin: 0;
  color: var(--apple-label, #f5f5f7);
  line-height: 1.45;
}

.memory-answer-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.48rem;
}

.memory-answer-grid .choice-button {
  min-width: 0;
  padding: 0.72rem 0.45rem;
}

[data-layout-morphing="true"] {
  overflow: clip;
  will-change: width, height, transform;
}

@media (max-width: 720px) {
  .memory-quadrant {
    top: 3.6rem;
    width: min(100%, 26.5rem);
  }

  .memory-answer-grid {
    grid-template-columns: 1fr;
  }
}

@media (prefers-reduced-motion: reduce) {
  .memory-quadrant,
  .memory-angle-label,
  .memory-value-token {
    transition-duration: 160ms !important;
  }
}

@media (max-width: 370px) {
  .transfer-angle-grid {
    grid-template-columns: repeat(3, minmax(0, 1fr));
  }
}

@media (prefers-reduced-motion: reduce) {
  .skill-proof-progress > span::after {
    transition-duration: 160ms !important;
  }
}

/* Learning-first shell: one prediction, optional memory support, honest transfer result. */
.hero-copy #lesson-title {
  max-width: 12ch;
  margin-inline: auto;
  font-size: clamp(2.45rem, 7vw, 4.75rem);
}

.hero-copy .hero-lead {
  margin: 1rem auto 1.5rem;
}

.hero-copy .hero-problem {
  margin-top: 1.5rem;
}

.baseline-card {
  width: min(100%, 36rem);
  margin: 2rem auto 0;
  padding: clamp(1rem, 3vw, 1.4rem);
  border: 1px solid var(--line-strong);
  border-radius: var(--radius-lg);
  background: color-mix(in srgb, var(--surface) 86%, transparent);
  text-align: left;
}

.baseline-kicker {
  color: var(--blue);
  font-size: 0.75rem;
  font-weight: 800;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.baseline-card > p {
  margin: 0.65rem 0 0;
  color: var(--cream-muted);
}

.math-inline {
  color: var(--cream);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  white-space: nowrap;
}

.baseline-choices {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.65rem;
  margin-top: 1rem;
}

.baseline-choices .choice-button {
  min-width: 0;
  text-align: center;
}

.baseline-choices .baseline-unknown {
  grid-column: 1 / -1;
  background: transparent;
  color: var(--cream-muted);
}

.baseline-choices .choice-button:disabled {
  opacity: 0.62;
}

.baseline-choices .choice-button.is-recorded {
  border-color: var(--blue);
  background: var(--blue-soft);
  color: var(--blue);
  opacity: 1;
}

.baseline-feedback {
  min-height: 1.5rem;
  font-size: 0.875rem;
}

.baseline-feedback.is-recorded {
  color: var(--blue);
}

.memory-aid-button {
  min-height: 2.75rem;
  margin-top: 0.65rem;
  padding: 0.5rem 0;
  border: 0;
  background: transparent;
  color: var(--cream-muted);
  cursor: pointer;
  font-size: 0.875rem;
  font-weight: 700;
  text-decoration: underline;
  text-decoration-color: var(--line-strong);
  text-underline-offset: 0.28em;
}

.memory-aid-button:hover:not(:disabled) {
  color: var(--cream);
  text-decoration-color: var(--cream);
}

.memory-aid {
  display: grid;
  grid-template-columns: 5.5rem minmax(0, 1fr);
  gap: 1rem;
  margin-top: 0.5rem;
  padding: 0.8rem;
  align-items: center;
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  background: var(--surface);
}

.memory-aid svg {
  width: 100%;
  max-height: 7.5rem;
  overflow: visible;
}

.memory-aid path {
  fill: none;
  stroke: var(--cream-muted);
  stroke-width: 3;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.memory-aid .memory-angle {
  stroke: var(--blue);
  stroke-width: 2;
}

.memory-aid text {
  fill: var(--cream-muted);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: 12px;
}

.memory-aid > div {
  display: grid;
  gap: 0.35rem;
}

.memory-aid small,
.memory-aid p {
  color: var(--cream-muted);
}

.memory-aid strong {
  color: var(--blue);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
}

.memory-aid p {
  margin: 0;
  font-size: 0.85rem;
}

.learning-proof {
  display: grid;
  max-width: 44rem;
  margin: 1.75rem auto 0;
  grid-template-columns: minmax(0, 1fr) auto minmax(0, 1fr);
  gap: 1rem;
  align-items: stretch;
}

.proof-item {
  display: grid;
  min-width: 0;
  padding: 1rem;
  border: 1px solid var(--line);
  border-radius: var(--radius-md);
  background: var(--surface-raised);
  text-align: left;
}

.proof-item small,
.proof-item span {
  color: var(--cream-dim);
  font-size: 0.75rem;
}

.proof-item strong {
  overflow-wrap: anywhere;
  color: var(--cream);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: clamp(1rem, 2.5vw, 1.25rem);
}

.proof-arrow {
  display: grid;
  place-items: center;
  color: var(--blue);
  font-size: 1.4rem;
}

#completion .result-meaning {
  color: var(--cream-dim);
  font-size: 0.875rem;
}

#completion .learning-proof {
  opacity: var(--melo-summary-finish);
  filter: blur(calc((1 - var(--melo-summary-finish)) * 5px));
  transform: translateY(calc((1 - var(--melo-summary-finish)) * 0.45rem));
}

@media (max-width: 600px) {
  .baseline-choices,
  .memory-aid {
    grid-template-columns: 1fr;
  }

  .baseline-choices .baseline-unknown {
    grid-column: auto;
  }

  .learning-proof {
    grid-template-columns: 1fr;
  }

  .proof-arrow {
    transform: rotate(90deg);
  }
}

@media (forced-colors: active) {
  .intersection-point,
  .solution-point::after,
  .coordinate-point {
    forced-color-adjust: none;
    background: CanvasText;
  }
}

/* v3 player shell: one visual thought at a time. */
.sr-only {
  position: absolute !important;
  width: 1px !important;
  height: 1px !important;
  padding: 0 !important;
  margin: -1px !important;
  overflow: hidden !important;
  clip: rect(0, 0, 0, 0) !important;
  white-space: nowrap !important;
  border: 0 !important;
}

.lesson-nav {
  position: fixed;
  right: 0;
  left: 0;
  will-change: transform;
  transition: transform 240ms var(--ease-out), box-shadow 180ms ease;
}

.lesson-nav.is-auto-hidden:not(:focus-within) {
  transform: translateY(calc(-100% + 3px));
}

.nav-main {
  min-height: 3.5rem;
}

.player-icon {
  position: relative;
  display: grid;
  width: 2.5rem;
  height: 2.5rem;
  place-items: center;
  padding: 0;
  border: 1px solid transparent;
  border-radius: 999px;
  background: transparent;
  color: var(--cream-muted);
  cursor: pointer;
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: 1rem;
  font-weight: 800;
}

.player-skip,
.player-speed {
  position: relative;
  min-height: 2.5rem;
  padding: 0 0.65rem;
  border: 1px solid transparent;
  border-radius: 999px;
  background: transparent;
  color: var(--cream-muted);
  cursor: pointer;
  font-size: 0.72rem;
  font-weight: 800;
  white-space: nowrap;
}

.player-speed {
  min-width: 2.9rem;
  color: var(--blue);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
}

.player-skip:hover:not(:disabled),
.player-speed:hover:not(:disabled) {
  border-color: var(--line-strong);
  background: var(--surface-raised);
  color: var(--cream);
}

.player-icon:hover:not(:disabled) {
  border-color: var(--line-strong);
  background: var(--surface-raised);
  color: var(--cream);
}

.player-icon[data-tooltip]::after,
.player-skip[data-tooltip]::after,
.player-speed[data-tooltip]::after {
  position: absolute;
  top: calc(100% + 0.45rem);
  left: 50%;
  z-index: 30;
  width: max-content;
  max-width: 12rem;
  padding: 0.35rem 0.5rem;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: var(--surface-raised);
  color: var(--cream);
  content: attr(data-tooltip);
  font-family: Rubik, ui-sans-serif, system-ui, sans-serif;
  font-size: 0.6875rem;
  font-weight: 650;
  opacity: 0;
  pointer-events: none;
  transform: translate(-50%, -0.2rem);
  transition: opacity 120ms ease, transform 120ms ease;
}

.player-icon[data-tooltip]:hover::after,
.player-icon[data-tooltip]:focus-visible::after,
.player-skip[data-tooltip]:hover::after,
.player-skip[data-tooltip]:focus-visible::after,
.player-speed[data-tooltip]:hover::after,
.player-speed[data-tooltip]:focus-visible::after {
  opacity: 1;
  transform: translate(-50%, 0);
}

.player-speed[data-tooltip]::after,
.voice-controls > :last-child[data-tooltip]::after {
  right: 0;
  left: auto;
  transform: translateY(-0.2rem);
}

.player-speed[data-tooltip]:hover::after,
.player-speed[data-tooltip]:focus-visible::after,
.voice-controls > :last-child[data-tooltip]:hover::after,
.voice-controls > :last-child[data-tooltip]:focus-visible::after {
  transform: translateY(0);
}

.media-timeline {
  display: grid;
  width: min(100% - 2rem, 70rem);
  min-height: 2.6rem;
  margin: 0 auto;
  grid-template-columns: 2.5rem minmax(8rem, 1fr) 2.5rem auto;
  gap: 0.65rem;
  align-items: center;
  padding-block: 0.28rem 0.45rem;
}

.timecode {
  color: var(--cream-dim);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: 0.6875rem;
  font-variant-numeric: tabular-nums;
}

.scrubber-wrap {
  position: relative;
  display: grid;
  min-height: 1.75rem;
  align-items: center;
}

#audio-scrubber {
  z-index: 2;
  width: 100%;
  height: 1.75rem;
  margin: 0;
  accent-color: var(--blue);
  cursor: ew-resize;
}

.cue-markers {
  position: absolute;
  right: 0.45rem;
  left: 0.45rem;
  top: 50%;
  z-index: 3;
  height: 0;
  pointer-events: none;
}

.cue-marker {
  position: absolute;
  top: -0.2rem;
  width: 0.38rem;
  height: 0.38rem;
  padding: 0;
  border: 0;
  border-radius: 50%;
  background: var(--cream);
  box-shadow: 0 0 0 2px var(--bg);
  opacity: 0.82;
  pointer-events: auto;
  transform: translateX(-50%);
}

.cue-marker:hover,
.cue-marker:focus-visible {
  background: var(--blue);
  transform: translateX(-50%) scale(1.5);
}

.audio-state {
  min-width: 4.5rem;
  color: var(--cream-muted);
  font-size: 0.6875rem;
  font-weight: 750;
  text-align: right;
}

body {
  padding-top: 6.6rem;
}

.lesson-page-chrome {
  position: fixed;
  z-index: 19;
  right: max(1.35rem, env(safe-area-inset-right));
  bottom: max(1.05rem, env(safe-area-inset-bottom));
  left: max(1.35rem, env(safe-area-inset-left));
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  color: #9aa08d;
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: 0.6875rem;
  letter-spacing: 0.025em;
  line-height: 1.2;
  pointer-events: none;
  text-transform: lowercase;
}

.lesson-page-hint,
.lesson-page-count {
  margin: 0;
  padding: 0.26rem 0.42rem;
  border-radius: 0.35rem;
  background: #0e121eb8;
  box-shadow: 0 0 0 1px #ffffff08;
  backdrop-filter: blur(8px);
}

.lesson-page-hint {
  transition: color 160ms ease, transform 240ms var(--ease-out);
}

.lesson-page-hint.is-blocked {
  color: var(--orange);
  transform: translateY(-0.15rem);
}

.lesson-page-hint.is-review-unlocked {
  color: var(--success);
}

.lesson-page-count {
  min-width: 3.5rem;
  color: var(--cream-dim);
  text-align: right;
}

.lesson-page-count #lesson-page-current {
  color: var(--cream);
}

.lesson-started .lesson-hero,
.lesson-started .lesson-section:not([hidden]) {
  scroll-snap-align: start;
  scroll-snap-stop: always;
}

.lesson-hero.is-memory-locked,
.lesson-section.is-memory-locked {
  pointer-events: none;
  user-select: none;
}

html.lesson-review-unlocked {
  scroll-snap-type: none;
  overscroll-behavior-y: auto;
}

.lesson-hero {
  display: grid;
  min-height: calc(100dvh - 6.6rem);
  grid-template-columns: 1fr;
  place-content: center;
  padding-block: var(--space-2xl);
  text-align: center;
}

.hero-copy {
  width: min(100%, 36rem);
  margin-inline: auto;
}

.hero-problem {
  display: grid;
  gap: 0.45rem;
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
}

.hero-problem span {
  font-size: clamp(2.5rem, 10vw, 5.5rem);
  font-weight: 850;
  letter-spacing: -0.07em;
  line-height: 1;
}

.hero-problem small {
  color: var(--cream-muted);
  font-size: 1rem;
}

.hero-actions {
  justify-content: center;
}

.hero-equation {
  display: none;
}

.coordinate-pair-visual {
  position: absolute;
  top: 0.8rem;
  right: 0.5rem;
  left: 0.5rem;
  z-index: 2;
  width: fit-content;
  max-width: calc(100% - 1rem);
  margin-inline: auto;
  padding: 0.45rem 0.65rem;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius-sm);
  background: var(--bg);
  color: var(--cream-muted);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: clamp(0.78rem, 2.5vw, 1rem);
  white-space: nowrap;
}

.coordinate-pair-visual strong {
  color: var(--blue);
}

.orientation-candidate {
  position: absolute;
  z-index: 1;
  display: block;
  opacity: 0.78;
  filter: none;
}

.candidate-horizontal {
  top: 23%;
  right: 4%;
  left: 4%;
  height: 2px;
  background: repeating-linear-gradient(90deg, var(--cream-muted) 0 0.65rem, transparent 0.65rem 1rem);
}

.candidate-vertical {
  top: 4%;
  bottom: 4%;
  left: 25%;
  width: 2px;
  background: repeating-linear-gradient(180deg, var(--cream-muted) 0 0.65rem, transparent 0.65rem 1rem);
}

.orientation-question-mark {
  position: absolute;
  top: calc(23% - 2.8rem);
  left: calc(25% + 0.8rem);
  z-index: 3;
  color: var(--orange);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: 2rem;
  font-weight: 850;
}

.axis-card.orientation-resolved .orientation-candidate,
.axis-card.orientation-resolved .orientation-question-mark {
  opacity: 0 !important;
  pointer-events: none;
}

.orientation-choice {
  display: inline-flex;
  align-items: center;
  gap: 0.7rem;
}

.choice-line {
  display: inline-block;
  flex: 0 0 auto;
  background: currentColor;
}

.choice-line-horizontal {
  width: 1.35rem;
  height: 2px;
}

.choice-line-vertical {
  width: 2px;
  height: 1.35rem;
  margin-inline: 0.65rem;
}

.step-index,
.step-copy > h2,
.step-copy > p:first-of-type:not(.question-copy),
.reason-chain,
.transcript {
  display: none;
}

.lesson-section {
  min-height: calc(100dvh - 6.6rem);
  scroll-margin-top: 6.6rem;
}

.lesson-section.is-narrating-step > .step-grid,
.lesson-section.is-narrating-step > .transfer-inner {
  grid-template-columns: 1fr;
}

.lesson-section.is-narrating-step > .step-grid .step-copy,
.lesson-section.is-narrating-step > .transfer-inner .step-copy {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  opacity: 0;
  pointer-events: none;
}

.lesson-section.is-narrating-step > .step-grid .visual-stage,
.lesson-section.is-narrating-step > .transfer-inner .visual-stage {
  width: min(100%, 54rem);
  margin-inline: auto;
}

.lesson-section.is-awaiting-action:not(.is-handoff-transitioning):not(.is-handoff-settled) > .step-grid .step-copy,
.lesson-section.is-awaiting-action:not(.is-handoff-transitioning):not(.is-handoff-settled) > .transfer-inner .step-copy {
  animation: action-panel-in 300ms var(--ease-out) both;
}

.lesson-section.is-handoff-transitioning {
  isolation: isolate;
}

.lesson-section.is-handoff-transitioning > .step-grid .visual-stage,
.lesson-section.is-handoff-transitioning > .transfer-inner .visual-stage {
  position: relative;
  z-index: 2;
  pointer-events: none;
  will-change: transform;
}

.lesson-section.is-handoff-transitioning > .step-grid .step-copy,
.lesson-section.is-handoff-transitioning > .transfer-inner .step-copy {
  animation: none !important;
  opacity: 0;
  filter: blur(7px);
  pointer-events: none;
  transform: translate3d(0, 0.8rem, 0);
  transition: none;
}

.lesson-section.is-handoff-transitioning.is-handoff-copy-visible > .step-grid .step-copy,
.lesson-section.is-handoff-transitioning.is-handoff-copy-visible > .transfer-inner .step-copy {
  opacity: 1;
  filter: blur(0);
  transform: translate3d(0, 0, 0);
  transition:
    opacity 260ms ease-out,
    filter 360ms var(--melo-morph, var(--ease-out)),
    transform 360ms var(--melo-morph, var(--ease-out));
}

.lesson-section.is-handoff-settled > .step-grid .step-copy,
.lesson-section.is-handoff-settled > .transfer-inner .step-copy {
  animation: none;
  opacity: 1;
  filter: none;
  transform: none;
}

.lesson-beat-history {
  display: grid;
  gap: 1rem;
  margin: 0 0 var(--space-2xl);
  padding: 1rem;
  overflow: hidden;
  border: 1px solid #a8e6b34d;
  border-radius: var(--radius-lg);
  background: linear-gradient(180deg, #15332255, #151a28cc);
  animation: beat-history-in 360ms var(--ease-out) both;
}

.beat-history-head {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr) auto;
  gap: 0.75rem 1rem;
  align-items: baseline;
}

.beat-history-label,
.beat-history-status {
  color: var(--success);
  font-size: 0.75rem;
  font-weight: 750;
}

.beat-history-label {
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.beat-history-head strong {
  color: var(--cream);
}

.lesson-beat-snapshot {
  gap: var(--space-lg);
  opacity: 0.78;
  pointer-events: none;
  filter: saturate(0.78);
}

.lesson-beat-history .visual-stage {
  min-height: 24rem;
}

.lesson-beat-history .step-copy {
  align-self: center;
}

.beat-history-summary {
  margin: 0;
  color: var(--cream-muted);
  font-size: 0.9rem;
}

#step-1[data-active-clip="line-explanation"] > .step-grid .question-copy,
#step-1[data-active-clip="line-explanation"] > .step-grid #orientation-choices,
#step-1[data-active-clip="line-explanation"] > .step-grid #orientation-feedback,
#step-3[data-active-clip="angle-explanation"] > .step-grid #angle-choices,
#step-3[data-active-clip="angle-explanation"] > .step-grid #angle-feedback,
#step-4[data-active-clip="answer-explanation"] > .step-grid #solution-feedback {
  display: none !important;
}

@keyframes beat-history-in {
  from { opacity: 0; transform: translateY(0.75rem); }
  to { opacity: 1; transform: translateY(0); }
}

@keyframes action-panel-in {
  from { opacity: 0; transform: translateY(0.5rem); }
  to { opacity: 1; transform: translateY(0); }
}

.narration-cue {
  max-width: min(22rem, calc(100% - 2rem));
  min-height: 2.2rem;
  padding: 0.4rem 0.6rem;
  border-color: #79d5ff3d;
  background: #0e121ed9;
  font-size: 0.75rem;
}

.visual-stage.has-narration-cue {
  padding-top: 3.75rem;
}

.circle-outline.is-cue-revealing,
.reference-arc.is-cue-revealing {
  animation: draw-path 700ms var(--ease-out) both;
}

.scan-line.is-cue-revealing,
.fixed-line.is-cue-revealing,
.radius-line.is-cue-revealing,
.solution-fixed-line.is-cue-revealing {
  animation: draw-line 560ms var(--ease-out) both;
  transform-box: fill-box;
  transform-origin: center;
}

.intersection-point.is-cue-revealing,
.solution-point.is-cue-revealing,
.coordinate-point.is-cue-revealing {
  animation: cue-point-in 420ms var(--ease-out) both;
  transform-box: fill-box;
  transform-origin: center;
}

@keyframes draw-path {
  from { stroke-dasharray: 1000; stroke-dashoffset: 1000; opacity: 1; }
  to { stroke-dasharray: 1000; stroke-dashoffset: 0; opacity: 1; }
}

@keyframes draw-line {
  from { opacity: 0; transform: scaleY(0); }
  to { opacity: 1; transform: scaleY(1); }
}

@keyframes cue-point-in {
  0% { opacity: 0; transform: scale(0.25); }
  70% { opacity: 1; transform: scale(1.18); }
  100% { opacity: 1; transform: scale(1); }
}

.manim-lab,
.manim-canvas {
  width: 100%;
  min-height: 31rem;
}

.manim-lab {
  position: relative;
}

.manim-motion-lab {
  overflow: hidden;
  border-radius: calc(var(--radius-lg) - 0.5rem);
  background:
    radial-gradient(circle at 50% 44%, #21304a 0, #151a28 58%, #10141f 100%);
}

.manim-motion-readout {
  position: absolute;
  top: 0.75rem;
  right: 0.75rem;
  display: grid;
  justify-items: end;
  gap: 0.12rem;
  max-width: min(72%, 24rem);
  padding: 0.62rem 0.75rem;
  border: 1px solid #79d5ff33;
  border-radius: 0.75rem;
  background: #10141fd9;
  box-shadow: 0 0.75rem 2rem #0005;
  pointer-events: none;
  backdrop-filter: blur(10px);
}

.visual-stage.has-narration-cue .manim-motion-readout {
  top: 4.5rem;
}

.manim-motion-kicker {
  color: var(--cream-dim);
  font-size: 0.65rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  line-height: 1.25;
  text-align: right;
  text-transform: uppercase;
}

.manim-motion-readout strong {
  color: var(--blue);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: clamp(1rem, 2.4vw, 1.45rem);
}

.manim-motion-readout > span:last-child {
  color: var(--cream-muted);
  font-size: 0.75rem;
}

.manim-canvas canvas {
  display: block;
  width: 100% !important;
  height: 100% !important;
  min-height: 31rem;
  cursor: grab;
}

.manim-canvas canvas:active {
  cursor: grabbing;
}

.manim-instruction {
  position: absolute;
  right: 1rem;
  bottom: 0.75rem;
  left: 1rem;
  margin: 0;
  color: var(--cream-dim);
  font-size: 0.75rem;
  text-align: center;
  opacity: 0;
  transition: opacity 180ms ease;
}

.manim-lab.is-interactive .manim-instruction {
  opacity: 1;
}

.circle-stage.is-manim-ready > #variation-circle,
.angle-stage.is-manim-ready #angle-svg-fallback {
  display: none;
}

.circle-stage.is-manim-ready .variation-control {
  position: relative;
  z-index: 2;
}

.manim-motion-lab.is-interactive .manim-motion-readout {
  border-color: #eb402355;
}

.manim-motion-lab.is-interactive .manim-motion-kicker {
  color: #f29a86;
}

.transfer-inner {
  grid-template-columns: minmax(20rem, 1.15fr) minmax(18rem, 0.85fr);
  align-items: center;
}

.transfer-stage {
  display: grid;
  min-height: 34rem;
  place-items: center;
  padding: 7rem var(--space-lg) var(--space-lg);
}

.transfer-stage > .narration-cue {
  top: auto;
  bottom: 1rem;
}

.transfer-stage > #transfer-circle-map {
  width: 100%;
  max-width: 30rem;
}

.transfer-brief {
  position: absolute;
  top: 1rem;
  left: 50%;
  z-index: 3;
  display: grid;
  min-width: min(90%, 20rem);
  grid-template-columns: 1fr auto;
  gap: 0.35rem 0.75rem;
  align-items: center;
  padding: 0.65rem 0.8rem;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius-sm);
  background: #0e121ee8;
  box-shadow: 0 0.75rem 2rem #05070c55;
  transform: translateX(-50%);
}

.transfer-equation {
  grid-row: 1 / span 2;
  color: var(--cream);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: 1.25rem;
  font-weight: 800;
}

.transfer-condition,
.transfer-coordinate {
  width: fit-content;
  justify-self: end;
  color: var(--cream-muted);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: 0.78rem;
  font-weight: 750;
}

.transfer-condition {
  color: var(--orange);
}

.transfer-coordinate {
  color: var(--blue);
}

.transfer-line {
  stroke: var(--blue);
  stroke-width: 3;
}

.transfer-copy {
  text-align: left;
}

.transfer-question {
  display: block !important;
  color: var(--cream-muted) !important;
}

.transcript-dialog {
  width: min(calc(100% - 2rem), 38rem);
  max-height: min(80dvh, 38rem);
  padding: 0;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius-lg);
  background: var(--surface-raised);
  color: var(--cream);
  box-shadow: 0 2rem 5rem #0009;
}

.transcript-dialog::backdrop {
  background: #05070cb8;
  backdrop-filter: blur(4px);
}

.dialog-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 1rem 1.25rem;
  border-bottom: 1px solid var(--line);
}

.dialog-head h2 {
  margin: 0;
  font-size: 1rem;
}

.transcript-dialog > p {
  margin: 0;
  padding: 1.25rem;
  color: var(--cream-muted);
}

@media (max-width: 1100px) {
  .lesson-hero,
  .lesson-section {
    width: min(100% - 2rem, 70rem);
  }
}

@media (max-width: 720px) {
  body {
    padding-top: 6.3rem;
    padding-bottom: 3.5rem;
  }

  .nav-main {
    width: min(100% - 1rem, 70rem);
    grid-template-columns: auto minmax(0, 1fr) auto;
  }

  #transcript-toggle,
  #voice-toggle {
    display: none;
  }

  .voice-controls {
    gap: 0;
  }

  .player-icon {
    width: 2.25rem;
    height: 2.25rem;
  }

  .player-skip {
    width: 2.25rem;
    min-height: 2.25rem;
    padding: 0;
    font-size: 0;
  }

  .player-skip::before {
    content: "↠";
    font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
    font-size: 1rem;
  }

  .player-speed {
    min-width: 2.45rem;
    min-height: 2.25rem;
    padding-inline: 0.25rem;
  }

  .media-timeline {
    width: min(100% - 1rem, 70rem);
    grid-template-columns: 2.25rem minmax(5rem, 1fr) 2.25rem;
    gap: 0.4rem;
  }

  .audio-state {
    display: none;
  }

  .lesson-page-chrome {
    right: max(0.65rem, env(safe-area-inset-right));
    bottom: max(0.65rem, env(safe-area-inset-bottom));
    left: max(0.65rem, env(safe-area-inset-left));
    font-size: 0.625rem;
  }

  .lesson-page-hint {
    max-width: calc(100vw - 5.5rem);
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
  }

  .lesson-hero,
  .lesson-section {
    width: min(100% - 1.25rem, 70rem);
  }

  .lesson-section {
    min-height: calc(100dvh - 6.3rem);
    padding-block: var(--space-lg) var(--space-2xl);
    scroll-margin-top: 6.3rem;
  }

  .section-toolbar {
    margin-bottom: 1rem;
  }

  .section-toolbar > span {
    margin-right: auto;
  }

  .lesson-beat-history {
    margin-bottom: var(--space-lg);
    padding: 0.75rem;
  }

  .beat-history-head {
    grid-template-columns: 1fr auto;
  }

  .beat-history-label {
    grid-column: 1 / -1;
  }

  .lesson-beat-history .visual-stage {
    min-height: 21rem;
  }

  .step-grid,
  .step-grid.visual-first {
    gap: var(--space-lg);
  }

  .transfer-inner {
    grid-template-columns: 1fr;
    gap: var(--space-lg);
  }

  .transfer-copy {
    text-align: center;
  }

  .transfer-stage {
    min-height: 28rem;
    padding-top: 6.8rem;
  }

  .transfer-brief {
    min-width: calc(100% - 1.5rem);
  }

  .manim-lab,
  .manim-canvas,
  .manim-canvas canvas {
    min-height: 23rem;
  }
}

/* Melo Quiet Motion — golden-scene vertical slice.
   One persistent coordinate surface follows the narrated line, then morphs
   into the learner's control without replacing the object or covering the math. */
#step-2 {
  --melo-ink: #050506;
  --melo-surface: #18181a;
  --melo-surface-raised: #242426;
  --melo-white: #f5f5f7;
  --melo-muted: #a1a1a8;
  --melo-blue: #2997ff;
  --melo-coral: #eb4023;
  --melo-morph: cubic-bezier(0.22, 1, 0.36, 1);
}

#step-2 .circle-stage {
  min-height: 37rem;
  padding: 0;
  overflow: hidden;
  border: 0;
  border-radius: 0;
  background: var(--melo-ink);
  isolation: isolate;
}

#step-2 .circle-stage::before {
  position: absolute;
  z-index: -1;
  inset: 8% 4% 17%;
  border-radius: 50%;
  background: radial-gradient(circle, #24252a 0, #101114 46%, transparent 72%);
  content: "";
  opacity: 0.68;
  pointer-events: none;
}

#step-2 .manim-motion-lab {
  overflow: visible;
  border-radius: 0;
  background: transparent;
}

#step-2 .manim-canvas,
#step-2 .manim-canvas canvas {
  min-height: 37rem;
}

#step-2 .narration-cue {
  top: 1rem;
  left: 1rem;
  min-height: 2.4rem;
  padding: 0.48rem 0.72rem;
  border: 0;
  border-radius: 999px;
  background: #1b1b1ef2;
  box-shadow: 0 6px 12px #0005;
  color: var(--melo-white);
  font-size: 0.75rem;
}

#step-2 .narration-cue-dot {
  width: 0.45rem;
  height: 0.45rem;
  background: var(--melo-blue);
  box-shadow: 0 0 0 0.22rem #2997ff24;
}

#step-2 .visual-stage.has-narration-cue {
  padding-top: 0;
}

.melo-coordinate-surface {
  --melo-anchor-x: 78%;
  position: absolute;
  z-index: 5;
  bottom: calc(100% - 4.5rem);
  left: var(--melo-anchor-x);
  width: 12.25rem;
  min-height: 3.5rem;
  overflow: hidden;
  border-radius: 999px;
  background: var(--melo-surface);
  box-shadow: 0 10px 20px #0008;
  color: var(--melo-white);
  pointer-events: none;
  transform: translateX(-50%);
  transition:
    left 360ms linear,
    bottom 580ms var(--melo-morph),
    width 580ms var(--melo-morph),
    min-height 580ms var(--melo-morph),
    border-radius 580ms var(--melo-morph),
    background-color 260ms ease,
    box-shadow 260ms ease;
}

.melo-coordinate-surface::after {
  position: absolute;
  inset: 0;
  border-radius: inherit;
  box-shadow: inset 0 1px #ffffff12;
  content: "";
  pointer-events: none;
}

.melo-coordinate-surface:not(.is-line-visible) {
  opacity: 0;
  filter: blur(6px);
}

.melo-coordinate-surface.is-line-visible {
  opacity: 1;
  filter: blur(0);
  transition:
    left 360ms linear,
    bottom 580ms var(--melo-morph),
    width 580ms var(--melo-morph),
    min-height 580ms var(--melo-morph),
    border-radius 580ms var(--melo-morph),
    background-color 260ms ease,
    box-shadow 260ms ease,
    opacity 180ms ease,
    filter 240ms ease;
}

.melo-coordinate-surface.is-interactive,
.melo-coordinate-surface:has(.variation-control:not(.is-cue-hidden)) {
  bottom: calc(100% - 7.25rem);
  left: 50%;
  width: calc(100% - 2rem);
  min-height: 7.1rem;
  border-radius: 16px;
  background: var(--melo-surface-raised);
  box-shadow: 0 12px 24px #0008;
  pointer-events: auto;
}

.manim-motion-readout {
  position: relative;
  inset: auto;
  display: flex;
  min-height: 3.5rem;
  align-items: center;
  gap: 0.65rem;
  width: 100%;
  max-width: none;
  padding: 0.55rem 0.8rem;
  border: 0;
  border-radius: 0;
  background: transparent;
  box-shadow: none;
  backdrop-filter: none;
  transition: opacity 180ms ease, filter 220ms ease;
}

#step-2 .visual-stage.has-narration-cue .melo-coordinate-surface:not(.is-interactive):not(:has(.variation-control:not(.is-cue-hidden))) .manim-motion-readout {
  top: auto;
  right: auto;
}

.melo-coordinate-mark {
  position: relative;
  width: 1.35rem;
  height: 2rem;
  flex: 0 0 auto;
}

.melo-coordinate-line {
  position: absolute;
  top: 0.12rem;
  bottom: 0.12rem;
  left: 50%;
  width: 2px;
  border-radius: 2px;
  background: var(--melo-blue);
  transform: translateX(-50%);
}

.melo-coordinate-dot {
  position: absolute;
  left: 50%;
  width: 0.38rem;
  height: 0.38rem;
  border-radius: 50%;
  background: var(--melo-white);
  box-shadow: 0 0 0 0.2rem #2997ff24;
  transform: translate(-50%, -50%);
}

.melo-coordinate-dot-top {
  top: 0.38rem;
}

.melo-coordinate-dot-bottom {
  bottom: 0;
}

.manim-motion-copy {
  display: grid;
  min-width: 0;
  gap: 0.02rem;
  line-height: 1.05;
}

.manim-motion-kicker {
  overflow: hidden;
  color: var(--melo-muted);
  font-size: 0.6rem;
  font-weight: 650;
  letter-spacing: 0;
  text-align: left;
  text-overflow: ellipsis;
  text-transform: none;
  white-space: nowrap;
}

.manim-motion-readout strong {
  color: var(--melo-white);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: 1rem;
  font-weight: 750;
  letter-spacing: -0.03em;
}

.manim-motion-readout .manim-motion-copy > span:last-child {
  overflow: hidden;
  color: var(--melo-muted);
  font-size: 0.62rem;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.melo-coordinate-surface.is-interactive .manim-motion-readout,
.melo-coordinate-surface:has(.variation-control:not(.is-cue-hidden)) .manim-motion-readout {
  position: absolute;
  top: 0.5rem;
  left: 0.65rem;
  width: auto;
  min-height: 1.65rem;
  padding: 0.15rem 0.35rem;
}

.melo-coordinate-surface.is-interactive .melo-coordinate-mark,
.melo-coordinate-surface:has(.variation-control:not(.is-cue-hidden)) .melo-coordinate-mark {
  width: 0.9rem;
  height: 1.35rem;
}

.melo-coordinate-surface.is-interactive .manim-motion-kicker,
.melo-coordinate-surface.is-interactive #manim-intersections-count,
.melo-coordinate-surface:has(.variation-control:not(.is-cue-hidden)) .manim-motion-kicker,
.melo-coordinate-surface:has(.variation-control:not(.is-cue-hidden)) #manim-intersections-count {
  display: none;
}

.melo-coordinate-surface .variation-control {
  position: absolute;
  z-index: 2;
  right: 0.9rem;
  bottom: 0.45rem;
  left: 0.9rem;
  display: block;
  height: 4.15rem;
  padding: 0;
  border: 0;
  background: transparent;
  opacity: 0;
  filter: blur(8px);
  pointer-events: none;
  transform: translateY(0.6rem);
  transition: opacity 180ms 150ms ease, filter 240ms 120ms ease, transform 320ms 100ms var(--melo-morph);
}

#step-2 .circle-stage.is-manim-ready .melo-coordinate-surface .variation-control {
  position: absolute;
  right: 0.9rem;
  bottom: 0.45rem;
  left: 0.9rem;
}

.melo-coordinate-surface.is-interactive .variation-control:not(.is-cue-hidden),
.melo-coordinate-surface:has(.variation-control:not(.is-cue-hidden)) .variation-control {
  opacity: 1;
  filter: blur(0);
  pointer-events: auto;
  transform: translateY(0);
}

.melo-coordinate-surface .variation-control.is-cue-revealing {
  animation: none;
}

.melo-coordinate-surface .variation-heading {
  position: absolute;
  right: 0;
  bottom: 2.7rem;
  left: 0;
  display: flex;
  min-height: 1.2rem;
  align-items: center;
  justify-content: space-between;
  gap: 0.65rem;
  padding-left: 0;
  color: var(--melo-muted);
  font-size: 0.72rem;
}

.melo-coordinate-surface .variation-heading label {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  overflow: hidden;
  clip: rect(0 0 0 0);
  white-space: nowrap;
  border: 0;
}

.melo-coordinate-surface .variation-heading strong,
.melo-coordinate-surface .variation-heading span {
  color: var(--melo-white);
}

.melo-coordinate-surface .variation-angle-readout {
  display: inline-flex;
  align-items: baseline;
  gap: 0.35rem;
  color: var(--melo-muted);
}

.melo-coordinate-surface .variation-angle-readout output {
  color: var(--melo-white);
  font-weight: 720;
}

.melo-coordinate-surface .variation-control input {
  position: absolute;
  right: 0;
  bottom: -0.15rem;
  left: 0;
  display: block;
  min-height: 2.75rem;
  margin: 0;
  appearance: none;
  background: transparent;
  accent-color: var(--melo-coral);
}

.melo-coordinate-surface .variation-control input::-webkit-slider-runnable-track {
  height: 0.25rem;
  border-radius: 999px;
  background: repeating-linear-gradient(to right, #77777e 0 1px, transparent 1px 8.3333%), #4c4c52;
}

.melo-coordinate-surface .variation-control input::-webkit-slider-thumb {
  width: 1.35rem;
  height: 1.35rem;
  margin-top: -0.55rem;
  appearance: none;
  border: 0;
  border-radius: 50%;
  background: var(--melo-coral);
  box-shadow: 0 0 0 0.28rem #eb402329, 0 4px 8px #0008;
}

.melo-coordinate-surface .variation-control input::-moz-range-track {
  height: 0.25rem;
  border-radius: 999px;
  background: repeating-linear-gradient(to right, #77777e 0 1px, transparent 1px 8.3333%), #4c4c52;
}

.melo-coordinate-surface .variation-control input::-moz-range-thumb {
  width: 1.35rem;
  height: 1.35rem;
  border: 0;
  border-radius: 50%;
  background: var(--melo-coral);
  box-shadow: 0 0 0 0.28rem #eb402329, 0 4px 8px #0008;
}

.melo-coordinate-surface .variation-control p {
  display: none;
}

.melo-coordinate-surface .angle-stop-scale {
  position: absolute;
  right: 0.68rem;
  bottom: 0;
  left: 0.68rem;
  height: 0.66rem;
  color: #a8a8af;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  font-size: 0.64rem;
  font-variant-numeric: tabular-nums;
  font-weight: 650;
  letter-spacing: 0;
  line-height: 1;
  pointer-events: none;
}

.melo-coordinate-surface .angle-stop-scale span {
  position: absolute;
  left: calc(var(--angle-stop) / 180 * 100%);
  color: inherit;
  transform: translateX(-50%);
  white-space: nowrap;
  transition: color 140ms ease, font-weight 140ms ease;
}

.melo-coordinate-surface .angle-stop-scale span:first-child {
  transform: none;
}

.melo-coordinate-surface .angle-stop-scale span:last-child {
  transform: translateX(-100%);
}

.melo-coordinate-surface .angle-stop-scale span.is-active {
  color: var(--melo-coral);
  font-weight: 800;
}

#step-2 .manim-instruction {
  position: static;
  max-height: 0;
  margin: 0;
  padding: 0 0.85rem;
  overflow: hidden;
  border-radius: 12px;
  background: var(--apple-surface, var(--melo-surface));
  color: var(--melo-muted);
  font-size: 0.82rem;
  line-height: 1.45;
  text-align: left;
  opacity: 0;
  transform: translateY(0.35rem);
  transition:
    max-height 320ms var(--melo-morph),
    margin 320ms var(--melo-morph),
    padding 320ms var(--melo-morph),
    opacity 180ms ease,
    transform 320ms var(--melo-morph);
}

#step-2 .step-grid:has(.melo-coordinate-surface.is-interactive) .manim-instruction,
#step-2 .step-grid:has(.variation-control:not(.is-cue-hidden)) .manim-instruction {
  max-height: 5rem;
  margin-top: var(--space-md);
  padding-block: 0.72rem;
  box-shadow: inset 0 0 0 1px #ffffff0d;
  opacity: 1;
  transform: translateY(0);
}

#step-2 .manim-canvas,
#step-2 #variation-circle {
  transition: transform 580ms var(--melo-morph), filter 220ms ease;
  transform: translateY(4.6rem) scale(0.84);
  transform-origin: 50% 0;
}

#step-2 .circle-stage:has(.melo-coordinate-surface.is-interactive) .manim-canvas,
#step-2 .circle-stage:has(.variation-control:not(.is-cue-hidden)) .manim-canvas,
#step-2 .circle-stage:has(.melo-coordinate-surface.is-interactive) #variation-circle,
#step-2 .circle-stage:has(.variation-control:not(.is-cue-hidden)) #variation-circle {
  transform: translateY(4.6rem) scale(0.84);
}

#step-2 .circle-stage:has(.melo-coordinate-surface.is-interactive) .narration-cue,
#step-2 .circle-stage:has(.variation-control:not(.is-cue-hidden)) .narration-cue,
#step-2 .circle-stage:has(.melo-coordinate-surface.is-line-visible) .narration-cue {
  opacity: 0;
  filter: blur(5px);
}

#step-2 .variation-control.is-cue-focused {
  filter: none;
}

#step-2 .circle-axis {
  stroke: #424248;
}

#step-2 .circle-outline,
#step-2 .intersection-point {
  stroke: var(--melo-white);
}

/* Step 2 — the labels belong to the moving geometry. They stay hidden while
   narration introduces the circle and appear only when manipulation unlocks. */
.variation-handle {
  fill: var(--melo-coral);
  stroke: var(--melo-ink);
  stroke-width: 3;
}

.intersection-annotation-layer {
  --intersection-x: 32.14%;
  --intersection-y-top: 19.08%;
  --intersection-y-bottom: 80.92%;
  --coordinate-label-x: 32.14%;
  position: absolute;
  z-index: 4;
  top: 0;
  left: 50%;
  width: min(100%, 32rem);
  aspect-ratio: 1;
  color: var(--melo-white);
  pointer-events: none;
  transform: translate(-50%, 4.6rem) scale(0.84);
  transform-origin: 50% 0;
  transition: transform 580ms var(--melo-morph), opacity 220ms ease, filter 240ms ease;
}

.intersection-annotation-layer--manim {
  display: none;
  inset: 0;
  left: 0;
  width: 100%;
  max-width: none;
  height: 100%;
  aspect-ratio: auto;
  transform: translateY(4.6rem) scale(0.84);
}

#step-2 .circle-stage.is-manim-ready .intersection-annotation-layer--manim {
  display: block;
}

#step-2 .circle-stage.is-manim-ready > .intersection-annotation-layer--svg {
  display: none;
}

.intersection-angle-tag,
.intersection-coordinate-tag {
  position: absolute;
  display: grid;
  width: max-content;
  max-width: 9.75rem;
  border: 1px solid #ffffff14;
  background: #18181ae8;
  box-shadow: 0 8px 18px #0008, inset 0 1px #ffffff0f;
  backdrop-filter: blur(10px);
}

.intersection-angle-tag {
  left: calc(var(--intersection-x) + 0.75rem);
  min-width: 6.6rem;
  grid-template-columns: auto auto;
  gap: 0.12rem 0.55rem;
  align-items: baseline;
  padding: 0.42rem 0.58rem;
  border-radius: 0.7rem;
  transform: translateY(-50%);
}

.intersection-angle-tag::before {
  position: absolute;
  top: 50%;
  right: 100%;
  width: 0.75rem;
  height: 1px;
  background: #f5f5f766;
  content: "";
}

.intersection-angle-tag--top {
  top: var(--intersection-y-top);
}

.intersection-angle-tag--bottom {
  top: var(--intersection-y-bottom);
}

.intersection-angle-tag strong {
  color: var(--melo-white);
  font-size: 0.86rem;
  font-weight: 700;
}

.intersection-angle-tag > span {
  color: var(--melo-blue);
  font-size: 0.72rem;
  font-weight: 700;
}

.intersection-annotation-layer.labels-on-left .intersection-angle-tag {
  left: calc(var(--intersection-x) - 0.75rem);
  transform: translate(-100%, -50%);
}

.intersection-annotation-layer.labels-on-left .intersection-angle-tag::before {
  right: auto;
  left: 100%;
}

.intersection-annotation-layer.is-tangent .intersection-angle-tag--top {
  top: calc(var(--intersection-y-top) - 3rem);
}

.intersection-annotation-layer.is-tangent .intersection-angle-tag--bottom {
  display: none;
}

.intersection-coordinate-tag {
  top: 50%;
  left: var(--coordinate-label-x);
  min-width: 7.6rem;
  gap: 0.06rem;
  padding: 0.42rem 0.58rem 0.46rem 0.74rem;
  border-color: #eb402344;
  border-radius: 0.72rem;
  transform: translate(-50%, 0.9rem);
}

.intersection-coordinate-tag::before {
  position: absolute;
  top: -1rem;
  left: 50%;
  width: 1px;
  height: 1rem;
  background: var(--melo-coral);
  content: "";
}

.intersection-coordinate-tag small {
  color: var(--melo-muted);
  font-size: 0.58rem;
  font-weight: 650;
  letter-spacing: 0.01em;
}

.intersection-coordinate-tag strong {
  color: var(--melo-white);
  font-size: 0.82rem;
  font-weight: 700;
}

#step-2 .katex {
  line-height: 1.05;
}

.math-choice .katex,
.equation-main .katex,
.final-answer .katex {
  font-size: 1em;
}

#step-2 .scan-line {
  stroke: var(--melo-blue);
}

@media (max-width: 720px) {
  #step-2 .circle-stage,
  #step-2 .manim-canvas,
  #step-2 .manim-canvas canvas {
    min-height: 29.5rem;
  }

  #step-2 .circle-stage::before {
    inset: 10% 0 21%;
  }

  .melo-coordinate-surface {
    bottom: calc(100% - 4.5rem);
  }

  .melo-coordinate-surface.is-interactive,
  .melo-coordinate-surface:has(.variation-control:not(.is-cue-hidden)) {
    top: 0.75rem;
    bottom: auto;
    width: calc(100% - 1.2rem);
    min-height: 6.75rem;
  }

  .melo-coordinate-surface .variation-heading {
    padding-left: 0;
  }

  .melo-coordinate-surface .angle-stop-scale {
    font-size: 0.58rem;
  }

  #step-2 .circle-stage:has(.melo-coordinate-surface.is-interactive) .manim-canvas,
  #step-2 .circle-stage:has(.variation-control:not(.is-cue-hidden)) .manim-canvas,
  #step-2 .circle-stage:has(.melo-coordinate-surface.is-interactive) #variation-circle,
  #step-2 .circle-stage:has(.variation-control:not(.is-cue-hidden)) #variation-circle {
    transform: translateY(8.2rem) scale(0.78);
  }

  #step-2 .circle-stage:has(.melo-coordinate-surface.is-interactive) > .intersection-annotation-layer--svg,
  #step-2 .circle-stage:has(.variation-control:not(.is-cue-hidden)) > .intersection-annotation-layer--svg {
    transform: translate(-50%, 8.2rem) scale(0.78);
  }

  #step-2 .circle-stage:has(.melo-coordinate-surface.is-interactive) .intersection-annotation-layer--manim,
  #step-2 .circle-stage:has(.variation-control:not(.is-cue-hidden)) .intersection-annotation-layer--manim {
    transform: translateY(8.2rem) scale(0.78);
  }

  .intersection-angle-tag {
    min-width: 5.6rem;
    gap: 0.08rem 0.38rem;
    padding: 0.34rem 0.44rem;
  }

  .intersection-angle-tag strong {
    font-size: 0.72rem;
  }

  .intersection-angle-tag > span {
    font-size: 0.64rem;
  }

  .intersection-coordinate-tag {
    min-width: 6.65rem;
    padding: 0.34rem 0.44rem 0.38rem 0.58rem;
  }

  .intersection-coordinate-tag small {
    font-size: 0.5rem;
  }

  .intersection-coordinate-tag strong {
    font-size: 0.72rem;
  }
}

@media (prefers-reduced-motion: reduce) {
  .melo-coordinate-surface,
  .melo-coordinate-surface.is-line-visible,
  .melo-coordinate-surface .variation-control,
  .manim-motion-readout {
    transition-duration: 180ms !important;
  }

  .intersection-annotation-layer {
    transition-duration: 180ms !important;
  }
}

/* Melo Quiet Motion — full lesson system.
   Every stage keeps one causal object on screen, then morphs that object into
   the learner's next control or result. The audio clock owns all progress. */
#step-1,
#step-2,
#step-3,
#step-4,
#step-5 {
  --melo-ink: #050506;
  --melo-surface: #18181a;
  --melo-surface-raised: #242426;
  --melo-white: #f5f5f7;
  --melo-muted: #a1a1a8;
  --melo-blue: #2997ff;
  --melo-coral: #eb4023;
  --melo-morph: cubic-bezier(0.22, 1, 0.36, 1);
}

.melo-motion-stage {
  min-height: 37rem;
  padding: 0;
  overflow: hidden;
  border: 0;
  border-radius: 0;
  background: var(--melo-ink);
  isolation: isolate;
}

.melo-motion-stage::before {
  position: absolute;
  z-index: -1;
  inset: 9% 4% 18%;
  border-radius: 50%;
  background: radial-gradient(circle, #24252a 0, #101114 48%, transparent 72%);
  content: "";
  opacity: 0.62;
  pointer-events: none;
}

#step-1 .narration-cue,
#step-3 .narration-cue,
#step-4 .narration-cue,
#step-5 .narration-cue {
  top: 1rem;
  left: 1rem;
  min-height: 2.4rem;
  padding: 0.48rem 0.72rem;
  border: 0;
  border-radius: 999px;
  background: #1b1b1ef2;
  box-shadow: 0 6px 12px #0005;
  color: var(--melo-white);
  font-size: 0.75rem;
}

#step-1 .narration-cue-dot,
#step-3 .narration-cue-dot,
#step-4 .narration-cue-dot,
#step-5 .narration-cue-dot {
  width: 0.45rem;
  height: 0.45rem;
  background: var(--melo-blue);
  box-shadow: 0 0 0 0.22rem #2997ff24;
}

#step-1 .visual-stage.has-narration-cue,
#step-3 .visual-stage.has-narration-cue,
#step-4 .visual-stage.has-narration-cue,
#step-5 .visual-stage.has-narration-cue {
  padding-top: 0;
}

/* Step 1 — the coordinate pair is the anchor; the vertical projection grows
   out of the same x coordinate instead of appearing as a separate card. */
#step-1 .axis-card {
  width: min(78%, 22rem);
  transform: translateY(-0.35rem);
}

#step-1 .axis-line,
#step-1 .axis-name,
#step-1 .coordinate-point,
#step-1 .coordinate-pair-visual,
#step-1 .orientation-candidate,
#step-1 .orientation-question-mark,
#step-1 .coordinate-drop,
#step-1 .coordinate-value {
  will-change: transform, opacity, filter;
}

#step-1 .axis-x {
  opacity: var(--melo-axes, 0);
  transform: scaleX(var(--melo-axes, 0));
  transform-origin: left center;
}

#step-1 .axis-y {
  opacity: var(--melo-axes, 0);
  transform: scaleY(var(--melo-axes, 0));
  transform-origin: center bottom;
}

#step-1 .axis-name {
  opacity: var(--melo-axes, 0);
  filter: brightness(calc(1 + var(--melo-x-focus, 0) * 0.8));
}

#step-1 .coordinate-point {
  border-width: 0;
  background: var(--melo-white);
  box-shadow: 0 0 0 calc(var(--melo-point, 0) * 0.28rem) #2997ff24;
  opacity: var(--melo-point, 0);
  transform: translate(-50%, -50%) scale(var(--melo-point, 0));
}

#step-1 .coordinate-pair-visual {
  top: auto;
  right: auto;
  bottom: 0.15rem;
  left: 50%;
  min-height: 3.35rem;
  display: flex;
  align-items: center;
  padding: 0.55rem 0.9rem;
  border: 0;
  border-radius: 999px;
  background: var(--melo-surface);
  box-shadow: 0 10px 20px #0008;
  color: var(--melo-muted);
  opacity: var(--melo-pair, 0);
  filter: blur(calc((1 - var(--melo-pair, 0)) * 6px)) brightness(calc(1 + var(--melo-pair-focus, 0) * 0.22));
  transform: translateX(-50%) scale(calc(0.82 + var(--melo-pair, 0) * 0.18));
  transform-origin: center;
}

#step-1 .coordinate-pair-visual::after {
  position: absolute;
  inset: 0;
  border-radius: inherit;
  box-shadow: inset 0 1px #ffffff12;
  content: "";
  pointer-events: none;
}

#step-1 .coordinate-pair-visual strong {
  color: color-mix(in srgb, var(--melo-blue) calc(68% + var(--melo-cos-focus, 0) * 32%), var(--melo-white));
  filter: drop-shadow(0 0 calc(var(--melo-cos-focus, 0) * 0.5rem) #2997ff99);
}

#step-1 .candidate-horizontal {
  background: var(--melo-muted);
  opacity: calc(var(--melo-horizontal, 0) * 0.72);
  transform: scaleX(var(--melo-horizontal, 0));
  transform-origin: left center;
}

#step-1 .candidate-vertical {
  background: var(--melo-muted);
  opacity: calc(var(--melo-vertical, 0) * 0.72);
  transform: scaleY(var(--melo-vertical, 0));
  transform-origin: center top;
}

#step-1 .orientation-question-mark {
  color: var(--melo-coral);
  opacity: var(--melo-question, 0);
  transform: translateY(calc((1 - var(--melo-question, 0)) * 0.55rem)) scale(calc(0.82 + var(--melo-question, 0) * 0.18));
}

#step-1 .coordinate-drop {
  background: var(--melo-blue);
  opacity: var(--melo-proof, 0);
  transform: translateX(-50%) scaleY(var(--melo-proof, 0));
  transform-origin: center top;
}

#step-1 .coordinate-value {
  color: var(--melo-white);
  opacity: var(--melo-proof, 0);
  filter: blur(calc((1 - var(--melo-proof, 0)) * 5px));
  transform: translate(-50%, calc((1 - var(--melo-proof, 0)) * 0.45rem));
}

#step-1 .axis-card.orientation-resolved .candidate-horizontal,
#step-1 .axis-card.orientation-resolved .candidate-vertical,
#step-1 .axis-card.orientation-resolved .orientation-question-mark {
  opacity: 0 !important;
}

#step-1 .coordinate-stage .narration-cue.is-visible {
  opacity: calc(1 - var(--melo-pair, 0));
  filter: none;
}

/* Step 3 — the compact reference-angle pill expands into the two symmetric
   constructions while the circle remains the same object behind it. */
#step-3 .manim-lab,
#step-3 .manim-canvas,
#step-3 .manim-canvas canvas,
#step-3 #angle-svg-fallback {
  min-height: 37rem;
}

#step-3 .manim-canvas,
#step-3 #angle-svg-fallback {
  transform: translateY(2.2rem) scale(0.75);
  transform-origin: 50% 50%;
  transition: transform 580ms var(--melo-morph);
}

.melo-angle-surface,
.melo-solution-surface {
  position: absolute;
  z-index: 5;
  top: 1rem;
  bottom: auto;
  left: 33.5%;
  display: flex;
  width: 12.25rem;
  min-height: 3.5rem;
  align-items: center;
  gap: 0.7rem;
  overflow: hidden;
  padding: 0.55rem 0.8rem;
  border-radius: 999px;
  background: var(--melo-surface);
  box-shadow: 0 10px 20px #0008;
  color: var(--melo-white);
  pointer-events: none;
  transform: translateX(-50%);
  transition:
    left 580ms var(--melo-morph),
    width 580ms var(--melo-morph),
    min-height 580ms var(--melo-morph),
    border-radius 580ms var(--melo-morph),
    background-color 260ms ease,
    box-shadow 260ms ease;
}

.melo-angle-surface::after,
.melo-solution-surface::after,
#step-5 .transfer-brief::after {
  position: absolute;
  inset: 0;
  border-radius: inherit;
  box-shadow: inset 0 1px #ffffff12;
  content: "";
  pointer-events: none;
}

.melo-angle-surface {
  opacity: var(--melo-angle-surface, 0);
  filter: blur(calc((1 - var(--melo-angle-surface, 0)) * 6px));
}

.melo-angle-surface.is-expanded {
  left: 50%;
  width: calc(100% - 2rem);
  min-height: 7.3rem;
  align-items: flex-start;
  border-radius: 16px;
  background: var(--melo-surface-raised);
}

#step-3 .angle-stage:has(.melo-angle-surface.is-expanded) .manim-canvas,
#step-3 .angle-stage:has(.melo-angle-surface.is-expanded) #angle-svg-fallback {
  transform: translateY(4.25rem) scale(0.66);
}

.melo-angle-glyph {
  position: relative;
  width: 1.7rem;
  height: 1.7rem;
  flex: 0 0 auto;
}

.melo-angle-glyph-axis,
.melo-angle-glyph-radius {
  position: absolute;
  bottom: 0.25rem;
  left: 0.18rem;
  width: 1.35rem;
  height: 2px;
  border-radius: 2px;
  background: var(--melo-muted);
  transform-origin: left center;
}

.melo-angle-glyph-radius {
  background: var(--melo-white);
  transform: rotate(-58deg);
}

.melo-angle-glyph-arc {
  position: absolute;
  bottom: 0.22rem;
  left: 0.25rem;
  width: 0.78rem;
  height: 0.78rem;
  border: 2px solid transparent;
  border-top-color: var(--melo-blue);
  border-radius: 50%;
  transform: rotate(-30deg);
}

.melo-angle-question-copy,
.melo-angle-answer-copy,
.melo-solution-progress,
.melo-solution-answer {
  min-width: 0;
}

.melo-angle-question-copy,
.melo-solution-progress {
  display: grid;
  gap: 0.03rem;
  line-height: 1.05;
  transition: opacity 180ms ease, filter 220ms ease;
}

.melo-angle-question-copy small,
.melo-angle-answer-copy > small,
.melo-solution-progress small,
.melo-solution-answer small,
.melo-transfer-result small {
  color: var(--melo-muted);
  font-size: 0.62rem;
  font-weight: 650;
}

.melo-angle-question-copy strong,
.melo-solution-progress strong {
  color: var(--melo-white);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: 1rem;
  letter-spacing: -0.03em;
}

.melo-angle-surface.is-expanded .melo-angle-question-copy {
  opacity: 0;
  filter: blur(5px);
}

.melo-angle-answer-copy {
  position: absolute;
  top: 0.7rem;
  right: 0.85rem;
  bottom: 0.7rem;
  left: 3.15rem;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.45rem 0.65rem;
  opacity: var(--melo-angle-answer, 0);
  filter: blur(calc((1 - var(--melo-angle-answer, 0)) * 6px));
}

.melo-angle-answer-copy > small {
  grid-column: 1 / -1;
}

.melo-angle-answer-copy > span {
  display: grid;
  gap: 0.18rem;
  padding-top: 0.45rem;
  border-top: 1px solid #ffffff17;
  opacity: var(--melo-angle-top, 0);
  transform: translateY(calc((1 - var(--melo-angle-top, 0)) * 0.45rem));
}

.melo-angle-answer-copy > span:last-child {
  opacity: var(--melo-angle-bottom, 0);
  transform: translateY(calc((1 - var(--melo-angle-bottom, 0)) * 0.45rem));
}

.melo-angle-answer-copy strong {
  color: var(--melo-muted);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: 0.7rem;
}

.melo-angle-answer-copy b {
  color: var(--melo-white);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: 1rem;
}

#step-3 .angle-stage .narration-cue.is-visible {
  opacity: calc(1 - var(--melo-angle-surface, 0));
  filter: none;
}

/* Step 4 — selected points fill the same small collector; the collector then
   opens into the final answer instead of spawning a disconnected result card. */
#step-4 .solution-circle {
  width: min(78%, 22.5rem);
  transform: translateY(2.2rem);
  transition: transform 580ms var(--melo-morph);
}

#step-4 .solution-axis-x {
  opacity: var(--melo-solution-base, 0);
  transform: scaleX(var(--melo-solution-base, 0));
  transform-origin: left center;
}

#step-4 .solution-axis-y {
  opacity: var(--melo-solution-base, 0);
  transform: scaleY(var(--melo-solution-base, 0));
  transform-origin: center bottom;
}

#step-4 .solution-ring {
  border-color: var(--melo-white);
  opacity: var(--melo-solution-base, 0);
  clip-path: inset(calc((1 - var(--melo-solution-base, 0)) * 50%) 0 0 0);
  transform: scale(calc(0.92 + var(--melo-solution-base, 0) * 0.08));
}

#step-4 .solution-fixed-line {
  background: var(--melo-blue);
  opacity: var(--melo-solution-line, 0);
  transform: scaleY(var(--melo-solution-line, 0));
  transform-origin: center top;
}

#step-4 .solution-point {
  border-width: 2px;
  border-color: var(--melo-white);
  background: var(--melo-ink);
  opacity: var(--melo-solution-points, 0);
  transform: translate(-50%, -50%) scale(var(--melo-solution-points, 0));
}

#step-4 .solution-point::after {
  background: var(--melo-white);
}

#step-4 .solution-point:hover:not(:disabled) {
  border-color: var(--melo-blue);
  transform: translate(-50%, -50%) scale(1.06);
}

#step-4 .solution-point:active:not(:disabled) {
  transform: translate(-50%, -50%) scale(0.96);
}

#step-4 .solution-point.is-selected {
  border-color: var(--melo-blue);
  background: #2997ff17;
}

#step-4 .solution-point.is-selected::after {
  background: var(--melo-blue);
}

.melo-solution-surface {
  left: 31.5%;
  opacity: var(--melo-solution-surface, 0);
  filter: blur(calc((1 - var(--melo-solution-surface, 0)) * 6px));
}

.melo-solution-surface.is-expanded {
  left: 50%;
  width: calc(100% - 2rem);
  min-height: 5.4rem;
  border-radius: 16px;
  background: var(--melo-surface-raised);
}

#step-4 .solution-stage:has(.melo-solution-surface.is-expanded) .solution-circle {
  transform: translateY(3.8rem) scale(0.88);
}

.melo-solution-glyph {
  position: relative;
  width: 1.4rem;
  height: 2rem;
  flex: 0 0 auto;
}

.melo-solution-line {
  position: absolute;
  top: 0.12rem;
  bottom: 0.12rem;
  left: 50%;
  width: 2px;
  border-radius: 2px;
  background: var(--melo-blue);
  transform: translateX(-50%);
}

.melo-solution-dot {
  position: absolute;
  left: 50%;
  width: 0.4rem;
  height: 0.4rem;
  border-radius: 50%;
  background: var(--melo-muted);
  box-shadow: 0 0 0 0.18rem #2997ff1c;
  transform: translate(-50%, -50%);
  transition: background-color 180ms ease, box-shadow 220ms ease, transform 220ms var(--melo-morph);
}

.melo-solution-dot-top {
  top: 0.4rem;
}

.melo-solution-dot-bottom {
  bottom: 0;
}

.melo-solution-surface.has-top .melo-solution-dot-top,
.melo-solution-surface.has-bottom .melo-solution-dot-bottom {
  background: var(--melo-white);
  box-shadow: 0 0 0 0.24rem #2997ff2d;
  transform: translate(-50%, -50%) scale(1.18);
}

.melo-solution-answer {
  position: absolute;
  top: 50%;
  right: 0.9rem;
  left: 3.15rem;
  display: grid;
  gap: 0.15rem;
  opacity: var(--melo-solution-answer, 0);
  filter: blur(calc((1 - var(--melo-solution-answer, 0)) * 6px));
  transform: translateY(-50%);
}

.melo-solution-answer strong {
  color: var(--melo-white);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: clamp(0.92rem, 3.7vw, 1.2rem);
  letter-spacing: -0.03em;
}

.melo-solution-surface.is-expanded .melo-solution-progress {
  opacity: 0;
  filter: blur(5px);
}

#step-4 .solution-stage .narration-cue.is-visible {
  opacity: calc(1 - var(--melo-solution-surface, 0));
  filter: none;
}

/* Step 5 — the equation pill gains interval and coordinate, then the same
   horizontal-line glyph resolves into the two transferred answers. */
#step-5 .transfer-stage > #transfer-circle-map {
  max-width: 27rem;
  transform: translateY(2rem) scale(0.82);
  transform-origin: 50% 50%;
}

#step-5 .transfer-inner {
  transition: grid-template-columns 680ms var(--melo-morph, cubic-bezier(.22, 1, .36, 1));
}

#step-5.is-circle-bridge .transfer-inner {
  grid-template-columns: minmax(0, 1fr);
}

#step-5 .transfer-stage.is-circle-bridge {
  min-height: min(78vh, 43rem);
}

#step-5 .transfer-stage.is-circle-bridge > #transfer-circle-map {
  width: min(calc(100% - 1rem), 38rem);
  transform: translateY(0);
}

#step-5 .transfer-axis,
#step-5 .transfer-circle {
  opacity: var(--melo-transfer-base, 0);
}

#step-5 .transfer-circle {
  stroke: var(--melo-white);
}

#step-5 .transfer-line {
  stroke: var(--melo-blue);
  stroke-dasharray: 1;
  stroke-dashoffset: calc(1 - var(--melo-transfer-line, 0));
}

#step-5 .transfer-point {
  opacity: var(--melo-transfer-points, 0);
  transform: scale(var(--melo-transfer-points, 0));
  transform-box: fill-box;
  transform-origin: center;
}

#step-5 .transfer-brief {
  top: 1rem;
  left: 50%;
  display: flex;
  width: 13.75rem;
  min-width: 0;
  min-height: 3.6rem;
  grid-template-columns: none;
  gap: 0.65rem;
  padding: 0.55rem 0.8rem;
  overflow: hidden;
  border: 0;
  border-radius: 999px;
  background: var(--melo-surface);
  box-shadow: 0 10px 20px #0008;
  opacity: var(--melo-transfer-equation, 0);
  filter: blur(calc((1 - var(--melo-transfer-equation, 0)) * 6px));
  transform: translateX(-50%) scale(calc(0.84 + var(--melo-transfer-equation, 0) * 0.16));
  transition:
    width 580ms var(--melo-morph),
    min-height 580ms var(--melo-morph),
    border-radius 580ms var(--melo-morph),
    background-color 260ms ease,
    opacity 180ms ease,
    filter 240ms ease,
    transform 320ms var(--melo-morph);
}

#step-5 .transfer-brief.is-expanded,
#step-5 .transfer-stage.transfer-resolved .transfer-brief {
  width: calc(100% - 2rem);
  min-height: 5.2rem;
  border-radius: 16px;
  background: var(--melo-surface-raised);
}

.melo-transfer-glyph {
  position: relative;
  width: 2rem;
  height: 1.4rem;
  flex: 0 0 auto;
}

.melo-transfer-line {
  position: absolute;
  top: 50%;
  right: 0;
  left: 0;
  height: 2px;
  border-radius: 2px;
  background: var(--melo-blue);
  transform: translateY(-50%);
}

.melo-transfer-dot {
  position: absolute;
  top: 50%;
  width: 0.4rem;
  height: 0.4rem;
  border-radius: 50%;
  background: var(--melo-white);
  box-shadow: 0 0 0 0.18rem #2997ff24;
  transform: translate(-50%, -50%);
}

.melo-transfer-dot-left {
  left: 25%;
}

.melo-transfer-dot-right {
  left: 75%;
}

#step-5 .transfer-equation {
  grid-row: auto;
  flex: 1 1 auto;
  font-size: 1rem;
  opacity: var(--melo-transfer-equation, 0);
}

#step-5 .transfer-condition,
#step-5 .transfer-coordinate {
  position: absolute;
  right: 0.85rem;
  opacity: 0;
  filter: blur(5px);
  transform: translateY(0.3rem);
  transition: opacity 180ms ease, filter 220ms ease, transform 300ms var(--melo-morph);
}

#step-5 .transfer-condition {
  top: 0.72rem;
  opacity: var(--melo-transfer-interval, 0);
  filter: blur(calc((1 - var(--melo-transfer-interval, 0)) * 5px));
  transform: translateY(calc((1 - var(--melo-transfer-interval, 0)) * 0.3rem));
}

#step-5 .transfer-coordinate {
  bottom: 0.72rem;
  opacity: var(--melo-transfer-coordinate, 0);
  filter: blur(calc((1 - var(--melo-transfer-coordinate, 0)) * 5px));
  transform: translateY(calc((1 - var(--melo-transfer-coordinate, 0)) * 0.3rem));
}

.melo-transfer-result {
  position: absolute;
  top: 50%;
  right: 0.85rem;
  left: 3.45rem;
  display: grid;
  gap: 0.12rem;
  opacity: 0;
  filter: blur(6px);
  transform: translateY(-42%);
  transition: opacity 220ms ease, filter 280ms ease, transform 420ms var(--melo-morph);
}

.melo-transfer-result strong {
  color: var(--melo-white);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: 1.05rem;
  letter-spacing: -0.03em;
}

#step-5 .transfer-stage.transfer-resolved .transfer-equation,
#step-5 .transfer-stage.transfer-resolved .transfer-condition,
#step-5 .transfer-stage.transfer-resolved .transfer-coordinate {
  opacity: 0;
  filter: blur(5px);
}

#step-5 .transfer-stage.transfer-resolved .melo-transfer-result {
  opacity: 1;
  filter: blur(0);
  transform: translateY(-50%);
}

#step-5 .transfer-stage .narration-cue.is-visible {
  opacity: calc(1 - var(--melo-transfer-equation, 0));
  filter: none;
}

#completion {
  --melo-summary-mark: 0;
  --melo-summary-coordinate: 0;
  --melo-summary-line: 0;
  --melo-summary-points: 0;
  --melo-summary-finish: 0;
  border: 0;
  border-radius: 0;
  background: var(--melo-ink);
}

#completion .completion-mark,
#completion h2 {
  opacity: var(--melo-summary-mark);
  filter: blur(calc((1 - var(--melo-summary-mark)) * 6px));
  transform: translateY(calc((1 - var(--melo-summary-mark)) * 0.6rem));
}

#completion .completion-chain span:nth-child(1) {
  opacity: var(--melo-summary-coordinate);
}

#completion .completion-chain span:nth-child(2),
#completion .completion-chain span:nth-child(3) {
  opacity: var(--melo-summary-line);
}

#completion .completion-chain span:nth-child(n+4) {
  opacity: var(--melo-summary-points);
}

#completion > p:not(.completion-mark),
#completion .completion-actions {
  opacity: var(--melo-summary-finish);
  filter: blur(calc((1 - var(--melo-summary-finish)) * 5px));
  transform: translateY(calc((1 - var(--melo-summary-finish)) * 0.45rem));
}

@media (max-width: 720px) {
  .melo-motion-stage,
  #step-3 .manim-lab,
  #step-3 .manim-canvas,
  #step-3 .manim-canvas canvas,
  #step-3 #angle-svg-fallback {
    min-height: 30rem;
  }

  .melo-motion-stage::before {
    inset: 10% 0 21%;
  }

  #step-1 .axis-card,
  #step-4 .solution-circle {
    width: min(78%, 19rem);
  }

  #step-3 .manim-canvas,
  #step-3 #angle-svg-fallback {
    transform: translateY(2rem) scale(0.72);
  }


  #step-3 .angle-stage:has(.melo-angle-surface.is-expanded) .manim-canvas,
  #step-3 .angle-stage:has(.melo-angle-surface.is-expanded) #angle-svg-fallback {
    transform: translateY(4rem) scale(0.63);
  }

  .melo-angle-surface.is-expanded,
  .melo-solution-surface.is-expanded,
  #step-5 .transfer-brief.is-expanded,
  #step-5 .transfer-stage.transfer-resolved .transfer-brief {
    width: calc(100% - 1.2rem);
  }

  #step-5 .transfer-stage {
    padding-top: 0;
  }

  #step-5 .transfer-stage > #transfer-circle-map {
    transform: translateY(1.7rem) scale(0.76);
  }
}

@media (prefers-reduced-motion: reduce) {
  #step-1 .axis-line,
  #step-1 .axis-name,
  #step-1 .coordinate-point,
  #step-1 .coordinate-pair-visual,
  #step-1 .orientation-candidate,
  #step-1 .orientation-question-mark,
  #step-1 .coordinate-drop,
  #step-1 .coordinate-value,
  .melo-angle-surface,
  .melo-angle-question-copy,
  .melo-solution-surface,
  .melo-solution-dot,
  #step-5 .transfer-brief,
  #step-5 .transfer-condition,
  #step-5 .transfer-coordinate,
  .melo-transfer-result {
    transition-duration: 180ms !important;
  }
}

/* Apple-inspired melo product system.
   Content stays opaque and quiet; translucent material belongs only to the
   player, navigation, and transient controls above the lesson. */
:root {
  --apple-black: #000000;
  --apple-canvas: #08080a;
  --apple-surface: #1c1c1e;
  --apple-surface-raised: #2c2c2e;
  --apple-label: #f5f5f7;
  --apple-secondary: #a1a1a6;
  --apple-tertiary: #77777e;
  --apple-separator: #38383a;
  --apple-blue: #2997ff;
  --apple-blue-pressed: #147ce5;
  --apple-red: #ff453a;
  --apple-green: #30d158;
  --apple-orange: #ff9f0a;
  --apple-control: #242426cc;
  --apple-control-hover: #343438e8;
  --apple-material: #161618c7;
  --apple-material-strong: #1f1f22ed;
  --apple-ease: cubic-bezier(0.22, 1, 0.36, 1);
  --apple-fast: 180ms;
  --apple-standard: 240ms;
}

html,
body {
  background: var(--apple-black);
}

body {
  color: var(--apple-label);
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", "Segoe UI", system-ui, sans-serif;
  font-size: 1rem;
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

button,
input,
summary {
  -webkit-tap-highlight-color: transparent;
}

button:focus-visible,
a:focus-visible,
input:focus-visible,
summary:focus-visible {
  outline: 3px solid var(--apple-blue);
  outline-offset: 3px;
}

.lesson-nav {
  border-bottom: 0;
  background: color-mix(in srgb, var(--apple-black) 74%, transparent);
  box-shadow: inset 0 -1px #ffffff14;
  -webkit-backdrop-filter: saturate(150%) blur(28px);
  backdrop-filter: saturate(150%) blur(28px);
}

.nav-main {
  width: min(100% - 2rem, 72rem);
  min-height: 3.75rem;
  padding-block: 0.35rem;
  grid-template-columns: auto minmax(0, 1fr);
  gap: 1rem;
}

.brand {
  color: var(--apple-label);
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Display", "Segoe UI", system-ui, sans-serif;
  font-size: 1.05rem;
  font-weight: 700;
  letter-spacing: -0.035em;
}

.brand span {
  color: var(--orange);
}

.timecode,
.audio-state {
  color: var(--apple-tertiary);
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", "Segoe UI", system-ui, sans-serif;
  font-variant-numeric: tabular-nums;
}

.voice-controls {
  min-height: 3rem;
  padding: 0.22rem;
  gap: 0.08rem;
  border-radius: 999px;
  background: var(--apple-control);
  box-shadow: inset 0 0 0 1px #ffffff12;
  -webkit-backdrop-filter: saturate(145%) blur(22px);
  backdrop-filter: saturate(145%) blur(22px);
}

.player-icon,
.player-skip,
.player-speed,
.nav-button {
  min-width: 2.75rem;
  min-height: 2.75rem;
  border: 0;
  border-radius: 999px;
  background: transparent;
  color: var(--apple-secondary);
  font-size: 0.75rem;
  font-weight: 600;
  transition:
    background-color var(--apple-fast) ease,
    color var(--apple-fast) ease,
    opacity var(--apple-fast) ease,
    transform 110ms ease;
}

.player-skip {
  padding-inline: 0.72rem;
}

.player-speed {
  color: var(--apple-blue);
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", "Segoe UI", system-ui, sans-serif;
  font-variant-numeric: tabular-nums;
}

.player-icon:hover:not(:disabled),
.player-skip:hover:not(:disabled),
.player-speed:hover:not(:disabled),
.nav-button:hover:not(:disabled) {
  border-color: transparent;
  background: var(--apple-control-hover);
  color: var(--apple-label);
}

.player-icon:active:not(:disabled),
.player-skip:active:not(:disabled),
.player-speed:active:not(:disabled),
.nav-button:active:not(:disabled) {
  transform: scale(0.94);
}

.nav-button[aria-pressed="true"] {
  background: #ffffff14;
  color: var(--apple-label);
}

.control-symbol {
  width: 1.16rem;
  height: 1.16rem;
  overflow: visible;
  fill: none;
  stroke: currentColor;
  stroke-width: 1.9;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.control-symbol-playback {
  fill: currentColor;
  stroke: none;
}

#play-pause-audio .control-symbol-play,
#play-pause-audio .control-symbol-pause {
  transform-box: fill-box;
  transform-origin: center;
  transition: opacity 120ms ease, transform 180ms var(--apple-ease);
}

#play-pause-audio[data-player-state="play"] .control-symbol-play,
#play-pause-audio[data-player-state="pause"] .control-symbol-pause {
  opacity: 1;
  transform: scale(1);
}

#play-pause-audio[data-player-state="play"] .control-symbol-pause,
#play-pause-audio[data-player-state="pause"] .control-symbol-play {
  opacity: 0;
  transform: scale(0.72);
}

.player-icon[data-tooltip]::after,
.player-skip[data-tooltip]::after,
.player-speed[data-tooltip]::after {
  top: calc(100% + 0.55rem);
  padding: 0.38rem 0.58rem;
  border: 0;
  border-radius: 8px;
  background: var(--apple-material-strong);
  box-shadow: 0 4px 8px #00000066;
  color: var(--apple-label);
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", "Segoe UI", system-ui, sans-serif;
  font-weight: 500;
  -webkit-backdrop-filter: blur(22px);
  backdrop-filter: blur(22px);
}

.progress-rail {
  height: 2px;
  background: #ffffff12;
}

.progress-rail span {
  background: var(--apple-blue);
  transition: transform 360ms var(--apple-ease);
}

.media-timeline {
  width: min(100% - 2rem, 72rem);
  min-height: 2.85rem;
  padding-block: 0.28rem 0.5rem;
  grid-template-columns: 2.35rem minmax(8rem, 1fr) 2.35rem auto;
}

.timecode,
.audio-state {
  font-size: 0.6875rem;
  font-weight: 500;
}

.scrubber-wrap {
  min-height: 2rem;
}

#audio-scrubber {
  width: 100%;
  height: 2rem;
  margin: 0;
  appearance: none;
  background: transparent;
  cursor: pointer;
}

#audio-scrubber::-webkit-slider-runnable-track {
  height: 0.24rem;
  border-radius: 999px;
  background: linear-gradient(
    to right,
    var(--apple-label) 0 var(--scrubber-progress, 0%),
    #ffffff38 var(--scrubber-progress, 0%) 100%
  );
}

#audio-scrubber::-webkit-slider-thumb {
  width: 0.92rem;
  height: 0.92rem;
  margin-top: -0.34rem;
  appearance: none;
  border: 0;
  border-radius: 50%;
  background: var(--apple-label);
  box-shadow: 0 2px 6px #00000073;
  transition: transform 120ms ease;
}

#audio-scrubber:hover::-webkit-slider-thumb,
#audio-scrubber:focus-visible::-webkit-slider-thumb {
  transform: scale(1.12);
}

#audio-scrubber::-moz-range-track {
  height: 0.24rem;
  border-radius: 999px;
  background: #ffffff38;
}

#audio-scrubber::-moz-range-progress {
  height: 0.24rem;
  border-radius: 999px;
  background: var(--apple-label);
}

#audio-scrubber::-moz-range-thumb {
  width: 0.92rem;
  height: 0.92rem;
  border: 0;
  border-radius: 50%;
  background: var(--apple-label);
  box-shadow: 0 2px 6px #00000073;
}

.cue-markers {
  right: 0.46rem;
  left: 0.46rem;
}

.cue-marker {
  top: -0.17rem;
  width: 0.34rem;
  height: 0.34rem;
  background: var(--apple-label);
  box-shadow: 0 0 0 2px var(--apple-black);
  opacity: 0.7;
}

.cue-marker:hover,
.cue-marker:focus-visible {
  background: var(--apple-blue);
  opacity: 1;
  transform: translateX(-50%) scale(1.35);
}

.lesson-page-chrome {
  color: var(--apple-secondary);
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", "Segoe UI", system-ui, sans-serif;
  font-size: 0.6875rem;
  letter-spacing: 0;
  text-transform: none;
}

.lesson-page-hint,
.lesson-page-count {
  min-height: 2rem;
  display: flex;
  align-items: center;
  padding: 0.38rem 0.62rem;
  border-radius: 999px;
  background: var(--apple-material);
  box-shadow: inset 0 0 0 1px #ffffff12;
  -webkit-backdrop-filter: saturate(145%) blur(22px);
  backdrop-filter: saturate(145%) blur(22px);
}

.lesson-page-hint.is-blocked {
  color: var(--apple-orange);
}

.lesson-page-hint > span {
  margin-right: 0.32rem;
}

.lesson-page-hint.is-review-unlocked {
  color: var(--apple-green);
}

.lesson-page-count,
.lesson-page-count #lesson-page-current {
  color: var(--apple-secondary);
  font-variant-numeric: tabular-nums;
}

.lesson-page-count {
  min-width: 0;
  min-height: 1.5rem;
  gap: 0.12rem;
  padding: 0.2rem 0.4rem;
  border-radius: 0.5rem;
  line-height: 1;
}

.lesson-page-divider {
  color: var(--apple-tertiary);
}

.lesson-page-count #lesson-page-current {
  color: var(--apple-label);
  font-weight: 650;
}

.lesson-hero,
.lesson-section {
  width: min(100% - 2rem, 68rem);
}

.lesson-hero {
  min-height: calc(100dvh - 6.6rem);
  padding-block: clamp(3rem, 8vh, 6.5rem);
}

.hero-copy {
  width: min(100%, 40rem);
}

.preview-label,
.step-index,
.equation-label,
.baseline-kicker {
  color: var(--apple-secondary);
  font-size: 0.8125rem;
  font-weight: 600;
  letter-spacing: -0.005em;
  text-transform: none;
}

.hero-copy #lesson-title {
  max-width: 11ch;
  color: var(--apple-label);
  font-size: clamp(3.15rem, 8vw, 5.5rem);
  font-weight: 700;
  letter-spacing: -0.04em;
  line-height: 0.98;
}

.hero-copy .hero-lead {
  max-width: 38rem;
  color: var(--apple-secondary);
  font-size: 1.125rem;
  line-height: 1.52;
}

.hero-problem,
.equation-main,
.equation-interval,
.coordinate-formula,
.angle-equations,
.math-inline,
.math-choice,
.final-answer,
.transfer-equation,
.proof-item strong {
  font-family: KaTeX_Main, "Times New Roman", serif;
}

.hero-problem span {
  color: var(--apple-label);
  font-size: clamp(2.8rem, 9vw, 5.2rem);
  font-weight: 500;
  letter-spacing: -0.035em;
}

.hero-problem small {
  color: var(--apple-secondary);
}

.baseline-card {
  margin-top: 2.5rem;
  padding: 1.25rem;
  border: 0;
  border-radius: 14px;
  background: var(--apple-surface);
  box-shadow: inset 0 0 0 1px #ffffff0d;
}

.baseline-card > p,
.hero-note,
.step-copy > p,
.revealed-explanation p,
.beat-history-summary,
.completion > p:not(.completion-mark),
.transcript-dialog > p {
  color: var(--apple-secondary);
}

.baseline-feedback,
.local-feedback,
.result-meaning {
  color: var(--apple-tertiary);
}

.primary-button,
.text-button,
.choice-button,
.section-replay,
.memory-aid-button {
  min-height: 2.75rem;
  font-size: 0.9375rem;
  font-weight: 600;
}

.primary-button {
  padding: 0.68rem 1.15rem;
  border: 0;
  border-radius: 999px;
  background: var(--apple-blue);
  color: #ffffff;
  box-shadow: none;
  transition: background-color var(--apple-fast) ease, transform 110ms ease;
}

.primary-button:hover:not(:disabled) {
  border-color: transparent;
  background: #3ca2ff;
}

.primary-button:active:not(:disabled) {
  border-color: transparent;
  background: var(--apple-blue-pressed);
  transform: scale(0.97);
}

.text-button,
.memory-aid-button {
  color: var(--apple-blue);
  text-decoration: none;
}

.text-button:hover,
.memory-aid-button:hover:not(:disabled) {
  color: #64b5ff;
  text-decoration: none;
}

.choice-row,
.choice-grid,
.transfer-choices,
.baseline-choices {
  gap: 0.65rem;
}

.choice-button {
  min-height: 3rem;
  border: 0;
  border-radius: 12px;
  background: var(--apple-surface);
  box-shadow: inset 0 0 0 1px #ffffff12;
  color: var(--apple-label);
  transition:
    background-color var(--apple-fast) ease,
    box-shadow var(--apple-fast) ease,
    color var(--apple-fast) ease,
    transform 110ms ease;
}

.choice-button:hover:not(:disabled) {
  border-color: transparent;
  background: var(--apple-surface-raised);
  box-shadow: inset 0 0 0 1px #ffffff24;
}

.choice-button.is-recorded,
.baseline-choices .choice-button.is-recorded {
  border-color: transparent;
  background: #0a2f52;
  box-shadow: inset 0 0 0 1px #2997ff8c;
  color: #8fcdff;
}

.choice-button.is-correct,
.choice-button.is-correct:disabled {
  border-color: transparent;
  background: #0e2d18;
  box-shadow: inset 0 0 0 1px #30d15899;
  color: #7de792;
}

.choice-button.is-wrong {
  border-color: transparent;
  background: #351412;
  box-shadow: inset 0 0 0 1px #ff453a99;
  color: #ff8a83;
}

.memory-aid {
  border: 0;
  border-radius: 12px;
  background: #242426;
  box-shadow: inset 0 0 0 1px #ffffff0d;
}

.lesson-section {
  border-top-color: #ffffff12;
}

.section-toolbar > span,
.beat-history-label,
.beat-history-status {
  color: var(--apple-tertiary);
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", "Segoe UI", system-ui, sans-serif;
  font-weight: 600;
  letter-spacing: 0;
  text-transform: none;
}

.section-replay {
  padding: 0.48rem 0.8rem;
  border: 0;
  border-radius: 999px;
  background: var(--apple-control);
  box-shadow: inset 0 0 0 1px #ffffff12;
  color: var(--apple-secondary);
  -webkit-backdrop-filter: blur(18px);
  backdrop-filter: blur(18px);
}

.section-replay:not(:disabled):hover,
.section-replay:not(:disabled):focus-visible {
  border-color: transparent;
  background: var(--apple-control-hover);
  color: var(--apple-label);
  transform: none;
}

.step-copy h2,
.transfer-copy h2,
.completion h2 {
  color: var(--apple-label);
  font-weight: 700;
  letter-spacing: -0.035em;
}

.step-copy strong {
  color: var(--apple-label);
}

.coordinate-formula,
.final-answer {
  border: 0;
  border-radius: 12px;
  background: var(--apple-surface);
  box-shadow: inset 0 0 0 1px #ffffff12;
}

.revealed-explanation {
  border-top-color: #ffffff12;
}

.visual-stage,
.completion {
  border: 0;
  border-radius: 14px;
  background: var(--apple-canvas);
  box-shadow: inset 0 0 0 1px #ffffff0a;
}

.visual-stage.is-narrating {
  border-color: transparent;
  box-shadow: inset 0 0 0 1px #2997ff52;
}

.axis-line,
.circle-axis,
.solution-axis {
  background: var(--apple-separator);
  stroke: var(--apple-separator);
}

.circle-outline,
.solution-ring {
  border-color: var(--apple-label);
  stroke: var(--apple-label);
}

.scan-line,
.fixed-line,
.solution-fixed-line,
.transfer-line,
.melo-coordinate-line,
.melo-solution-line,
.melo-transfer-line {
  background: var(--apple-blue);
  stroke: var(--apple-blue);
}

.candidate-horizontal {
  height: 0;
  border-top: 2px dashed var(--apple-secondary);
  background: none;
}

.candidate-vertical {
  width: 0;
  border-left: 2px dashed var(--apple-secondary);
  background: none;
}

.narration-cue,
#step-2 .narration-cue {
  border: 0;
  border-radius: 999px;
  background: var(--apple-material-strong);
  box-shadow: 0 4px 8px #00000066;
  color: var(--apple-label);
  -webkit-backdrop-filter: saturate(140%) blur(20px);
  backdrop-filter: saturate(140%) blur(20px);
}

.narration-cue-dot {
  background: var(--apple-blue);
  box-shadow: 0 0 0 0.2rem #2997ff2b;
}

.lesson-beat-history {
  padding: 1rem;
  border: 0;
  border-radius: 14px;
  background: #121214;
  box-shadow: inset 0 0 0 1px #ffffff0d;
}

.beat-history-status {
  color: var(--apple-green);
}

.reason-chain span:nth-child(odd),
.completion-chain span:nth-child(odd) {
  border: 0;
  background: var(--apple-surface);
  box-shadow: inset 0 0 0 1px #ffffff12;
  color: var(--apple-label);
}

.manim-motion-lab,
#step-2 .circle-stage,
#step-3 .angle-stage,
#step-4 .solution-stage,
#step-5 .transfer-stage {
  background-color: var(--apple-canvas);
}

.melo-coordinate-surface,
.melo-angle-surface,
.melo-solution-surface,
#step-5 .transfer-brief {
  background: var(--apple-surface);
  box-shadow: 0 8px 16px #00000080, inset 0 1px #ffffff12;
}

.melo-coordinate-surface.is-interactive,
.melo-coordinate-surface:has(.variation-control:not(.is-cue-hidden)),
.melo-angle-surface.is-expanded,
.melo-solution-surface.is-expanded,
#step-5 .transfer-brief.is-expanded,
#step-5 .transfer-stage.transfer-resolved .transfer-brief {
  border-radius: 14px;
  background: var(--apple-surface-raised);
}

.melo-coordinate-surface .variation-control input::-webkit-slider-runnable-track {
  height: 0.25rem;
  background: #5a5a5f;
}

.melo-coordinate-surface .variation-control input::-moz-range-track {
  height: 0.25rem;
  background: #5a5a5f;
}

.melo-coordinate-surface .variation-control input::-webkit-slider-thumb,
.melo-coordinate-surface .variation-control input::-moz-range-thumb {
  background: var(--orange);
  box-shadow: 0 0 0 0.24rem #eb402329, 0 3px 6px #00000073;
}

.intersection-angle-tag,
.intersection-coordinate-tag {
  border: 0;
  background: var(--apple-material-strong);
  box-shadow: 0 4px 8px #00000073, inset 0 0 0 1px #ffffff12;
  -webkit-backdrop-filter: saturate(140%) blur(20px);
  backdrop-filter: saturate(140%) blur(20px);
}

.intersection-angle-tag strong,
.intersection-coordinate-tag strong,
.manim-motion-readout strong,
.melo-solution-answer strong,
.melo-transfer-result strong {
  color: var(--apple-label);
  font-family: KaTeX_Main, "Times New Roman", serif;
}

.intersection-angle-tag > span,
.reference-label,
.coordinate-value,
.axis-name-x {
  color: var(--apple-blue);
  fill: var(--apple-blue);
}

.transcript-dialog {
  border: 0;
  border-radius: 16px;
  background: var(--apple-material-strong);
  box-shadow: 0 24px 48px #00000099;
  color: var(--apple-label);
  -webkit-backdrop-filter: saturate(145%) blur(30px);
  backdrop-filter: saturate(145%) blur(30px);
}

.transcript-dialog::backdrop {
  background: #00000085;
  -webkit-backdrop-filter: blur(8px);
  backdrop-filter: blur(8px);
}

.dialog-head {
  border-bottom-color: #ffffff14;
}

.learning-proof {
  gap: 0.75rem;
}

.proof-item {
  border: 0;
  border-radius: 12px;
  background: var(--apple-surface);
  box-shadow: inset 0 0 0 1px #ffffff0d;
}

.proof-item small,
.proof-item span {
  color: var(--apple-tertiary);
}

.proof-arrow {
  color: var(--apple-blue);
}

.completion {
  background: var(--apple-black);
  box-shadow: none;
}

.completion-mark {
  border: 0;
  background: var(--apple-green);
  color: #051108;
  box-shadow: none;
}

.review-unlocked-note {
  color: var(--apple-green) !important;
}

@media (max-width: 720px) {
  .nav-main {
    width: min(100% - 0.75rem, 72rem);
    gap: 0.35rem;
  }

  .brand {
    font-size: 0.95rem;
  }

  .voice-controls {
    padding: 0.12rem;
  }

  .player-icon,
  .player-skip,
  .player-speed,
  .nav-button {
    min-width: 2.5rem;
    min-height: 2.5rem;
  }

  .player-skip {
    width: 2.5rem;
    padding: 0;
    font-size: 0;
  }

  .media-timeline {
    width: min(100% - 1rem, 72rem);
  }

  .lesson-hero,
  .lesson-section {
    width: min(100% - 1rem, 68rem);
  }

  .lesson-hero {
    padding-block: 2.5rem 4rem;
  }

  .hero-copy #lesson-title {
    font-size: clamp(2.75rem, 14vw, 4.35rem);
  }

  .hero-copy .hero-lead {
    font-size: 1rem;
  }

  .baseline-card {
    padding: 1rem;
  }

  .baseline-choices,
  .choice-grid,
  .transfer-choices {
    grid-template-columns: 1fr;
  }

  .choice-button {
    min-height: 3.25rem;
  }

  .visual-stage,
  .completion {
    border-radius: 12px;
  }

  .lesson-page-hint {
    min-height: 1.85rem;
    padding: 0.32rem 0.52rem;
  }

  .lesson-page-count {
    min-height: 1.45rem;
    padding: 0.18rem 0.36rem;
  }
}

@media (max-width: 359px) {
  /* Keep every frequent-angle anchor without forcing nine labels into a
     280px track. The omitted labels remain visible as ticks; the live
     readout above the track always names the exact selected angle. */
  .melo-coordinate-surface .angle-stop-scale span:is(
    [data-angle-stop="30"],
    [data-angle-stop="60"],
    [data-angle-stop="120"],
    [data-angle-stop="150"]
  ) {
    width: 0.22rem;
    height: 0.22rem;
    overflow: hidden;
    border-radius: 50%;
    background: currentColor;
    color: var(--apple-tertiary);
    font-size: 0;
    transform: translate(-50%, 0.08rem);
  }

  .melo-coordinate-surface .angle-stop-scale span:is(
    [data-angle-stop="30"],
    [data-angle-stop="60"],
    [data-angle-stop="120"],
    [data-angle-stop="150"]
  ).is-active {
    background: var(--orange);
    color: var(--orange);
  }
}

/* Brandbook-style sealed lesson deck.
   During learning the document itself never scrolls: exactly one page owns
   vertical scrolling, and completed pages are removed from painting as well
   as from focus/accessibility. The full document flow returns after transfer. */
html.lesson-flow-active {
  height: 100%;
  overflow: hidden;
  overscroll-behavior: none;
  scroll-behavior: auto;
  scroll-snap-type: none;
}

html.lesson-flow-active body {
  height: 100dvh;
  min-height: 0;
  overflow: hidden;
}

html.lesson-flow-active #lesson-main {
  position: fixed;
  z-index: 0;
  top: 6.6rem;
  right: 0;
  bottom: 0;
  left: 0;
  overflow: clip;
  background: var(--apple-black);
  contain: layout paint;
  isolation: isolate;
}

html.lesson-flow-active #lesson-main > .lesson-hero,
html.lesson-flow-active #lesson-main > .lesson-section {
  position: absolute;
  inset: 0 auto 0 50%;
  width: min(100% - 2rem, 68rem);
  height: auto;
  min-height: 0;
  margin: 0;
  overflow-x: clip;
  overflow-y: auto;
  border-top: 0;
  background: var(--apple-black);
  opacity: 0;
  overscroll-behavior: contain;
  pointer-events: none;
  scrollbar-gutter: stable both-edges;
  touch-action: pan-y;
  transform: translate3d(-50%, 100%, 0);
  transition:
    transform 720ms cubic-bezier(0.22, 1, 0.36, 1),
    opacity 420ms ease-out,
    visibility 0s linear 720ms;
  visibility: hidden;
  will-change: transform, opacity;
  -webkit-overflow-scrolling: touch;
  overflow-anchor: none;
}

html.lesson-flow-active #lesson-main > :is(.lesson-hero, .lesson-section).is-current,
html.lesson-flow-active #lesson-main > :is(.lesson-hero, .lesson-section).is-opening,
html.lesson-flow-active #lesson-main > :is(.lesson-hero, .lesson-section).is-step-exiting {
  visibility: visible;
  transition-delay: 0s;
}

html.lesson-flow-active #lesson-main > :is(.lesson-hero, .lesson-section).is-current:not(.is-opening):not(.is-step-exiting) {
  z-index: 2;
  opacity: 1;
  pointer-events: auto;
  transform: translate3d(-50%, 0, 0);
}

html.lesson-flow-active #lesson-main > :is(.lesson-hero, .lesson-section).is-opening {
  z-index: 3;
  opacity: 0.72;
  transform: translate3d(-50%, 100%, 0);
}

html.lesson-flow-active #lesson-main > :is(.lesson-hero, .lesson-section).is-opening[data-transition-direction="backward"] {
  transform: translate3d(-50%, -100%, 0);
}

html.lesson-flow-active #lesson-main > :is(.lesson-hero, .lesson-section).is-step-exiting {
  z-index: 1;
  opacity: 0.42;
  pointer-events: none;
  transform: translate3d(-50%, -100%, 0);
}

html.lesson-flow-active #lesson-main > :is(.lesson-hero, .lesson-section).is-step-exiting[data-transition-direction="backward"] {
  transform: translate3d(-50%, 100%, 0);
}

html.lesson-flow-active #lesson-main > :is(.lesson-hero, .lesson-section).is-memory-locked {
  z-index: -1;
  content-visibility: hidden;
  opacity: 0;
  pointer-events: none;
  transform: translate3d(-50%, -100%, 0);
  transition: none;
  user-select: none;
  visibility: hidden;
}

html.lesson-step-switching #lesson-main {
  pointer-events: none;
}

@media (max-width: 720px) {
  html.lesson-flow-active #lesson-main {
    top: 6.3rem;
  }

  html.lesson-flow-active #lesson-main > .lesson-hero,
  html.lesson-flow-active #lesson-main > .lesson-section {
    width: min(100% - 1rem, 68rem);
    padding-bottom: max(4rem, calc(3rem + env(safe-area-inset-bottom)));
    scrollbar-gutter: auto;
  }
}

@media (prefers-reduced-motion: reduce) {
  html.lesson-flow-active #lesson-main > :is(.lesson-hero, .lesson-section) {
    transform: translate3d(-50%, 0, 0);
    transition: opacity 120ms linear, visibility 0s linear 120ms;
  }

  html.lesson-flow-active #lesson-main > :is(.lesson-hero, .lesson-section).is-opening,
  html.lesson-flow-active #lesson-main > :is(.lesson-hero, .lesson-section).is-step-exiting {
    opacity: 0;
    transform: translate3d(-50%, 0, 0);
  }
}

@media (prefers-reduced-transparency: reduce) {
  .lesson-nav,
  .voice-controls,
  .lesson-page-hint,
  .lesson-page-count,
  .section-replay,
  .narration-cue,
  .intersection-angle-tag,
  .intersection-coordinate-tag,
  .transcript-dialog {
    background: #1c1c1e;
    -webkit-backdrop-filter: none;
    backdrop-filter: none;
  }
}

@media (prefers-contrast: more) {
  :root {
    --apple-secondary: #d1d1d6;
    --apple-tertiary: #b0b0b5;
    --apple-separator: #636366;
  }

  .voice-controls,
  .lesson-page-hint,
  .lesson-page-count,
  .section-replay,
  .choice-button,
  .baseline-card,
  .visual-stage {
    box-shadow: inset 0 0 0 1px #ffffff42;
  }
}

@media (prefers-reduced-motion: reduce) {
  #play-pause-audio .control-symbol-play,
  #play-pause-audio .control-symbol-pause,
  #audio-scrubber::-webkit-slider-thumb {
    transition-duration: 1ms;
  }
}

/* ENT-direct lesson pass: every spoken object stays visible, named x, and
   solvable from the circle without an unspoken reference-angle prerequisite. */
.angle-pair-choices .choice-button {
  display: flex;
  min-height: 3.25rem;
  align-items: center;
  justify-content: center;
  gap: 0.7rem;
}

.angle-stage[data-renderer="svg"] .manim-lab,
.angle-stage[data-renderer="svg"] .melo-angle-surface {
  display: none !important;
}

#step-3 .angle-stage[data-renderer="svg"] #angle-svg-fallback {
  position: absolute;
  top: 50%;
  left: 50%;
  z-index: 2;
  display: block !important;
  width: min(calc(100% - 1rem), 33rem);
  height: auto;
  min-height: 0;
  aspect-ratio: 1;
  opacity: 1;
  transform: translate(-50%, -50%) !important;
}

#step-3 .radius-line {
  stroke: var(--apple-secondary);
  stroke-width: 2.5;
}

#step-3 .radius-top {
  opacity: var(--melo-angle-degree-top, 0);
}

#step-3 .radius-bottom {
  opacity: var(--melo-angle-degree-bottom, 0);
}

.angle-reading-layer {
  position: absolute;
  top: 50%;
  left: 50%;
  z-index: 4;
  width: min(calc(100% - 1rem), 33rem);
  aspect-ratio: 1;
  pointer-events: none;
  transform: translate(-50%, -50%);
}

.angle-reading-label {
  position: absolute;
  display: grid;
  min-width: 6.25rem;
  justify-items: center;
  gap: 0.15rem;
  padding: 0.55rem 0.7rem;
  border-radius: 14px;
  background: #1c1c1ef2;
  color: var(--apple-label);
  box-shadow: 0 4px 8px #0008;
  transform: translate(-50%, -50%);
}

.angle-reading-top {
  top: 19%;
  left: 23%;
  opacity: var(--melo-angle-degree-top, 0);
}

.angle-reading-bottom {
  top: 81%;
  left: 23%;
  opacity: var(--melo-angle-degree-bottom, 0);
}

.angle-reading-degrees {
  color: var(--apple-secondary);
  font-size: 0.82rem;
}

.angle-reading-radians {
  color: var(--apple-blue);
  font-size: 1.05rem;
}

.angle-reading-top .angle-reading-radians {
  opacity: var(--melo-angle-radian-top, 0);
}

.angle-reading-bottom .angle-reading-radians {
  opacity: var(--melo-angle-radian-bottom, 0);
}

.angle-reading-equation {
  position: absolute;
  bottom: 1rem;
  left: 50%;
  padding: 0.5rem 0.75rem;
  border-radius: 999px;
  background: #1c1c1ef2;
  color: var(--apple-label);
  opacity: var(--melo-angle-reading-base, 0);
  transform: translateX(-50%);
}

.solution-turn-runner {
  position: absolute;
  top: 50%;
  left: 50%;
  z-index: 5;
  width: 0.9rem;
  height: 0.9rem;
  border-radius: 50%;
  background: var(--apple-orange);
  box-shadow: 0 0 0 0.28rem #ff9f0a24;
  opacity: var(--melo-solution-turn, 0);
  transform:
    translate(-50%, -50%)
    rotate(calc(-120deg + var(--melo-solution-turn, 0) * 360deg))
    translateX(min(9.6rem, 38vw));
}

.solution-turn-copy {
  position: absolute;
  top: 52%;
  bottom: auto;
  left: 50%;
  z-index: 5;
  display: grid;
  width: min(72%, 12rem);
  justify-items: center;
  padding: 0.42rem 0.55rem;
  border-radius: 12px;
  background: #1c1c1ef2;
  color: var(--apple-label);
  opacity: var(--melo-turn-meaning, 0);
  transform: translate(-50%, -50%) translateY(calc((1 - var(--melo-turn-meaning, 0)) * 0.5rem));
}

.solution-turn-copy > span {
  color: var(--apple-orange);
  font-size: 1.15rem;
  font-weight: 700;
}

.solution-turn-copy small {
  color: var(--apple-secondary);
  text-align: center;
}

#step-5 .transfer-stage {
  min-height: 36rem;
}

/* The transfer scene already exposes the exact equation/circle named by the
   narration. Never cover them with the generic cue material. */
#step-5 .narration-cue {
  display: none !important;
}

#step-5 .transfer-stage > #transfer-circle-map {
  max-width: 28rem;
  transform: translateY(1.7rem) scale(0.8);
}

#step-5 .transfer-brief,
#step-5 .transfer-brief.is-expanded,
#step-5 .transfer-stage.transfer-resolved .transfer-brief {
  top: 0.8rem;
  display: grid;
  width: min(calc(100% - 2rem), 26rem);
  min-height: 4.35rem;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: 0.15rem 0.8rem;
  align-content: center;
  padding: 0.65rem 0.9rem;
  border-radius: 14px;
  background: #1c1c1ef2;
  box-shadow: 0 4px 8px #0008;
  transform: translateX(-50%);
}

#step-5 .transfer-equation {
  grid-row: 1 / span 2;
  align-self: center;
}

#step-5 .transfer-condition,
#step-5 .transfer-coordinate {
  position: static;
  justify-self: end;
  transform: none;
}

#step-5 .transfer-line-candidate {
  fill: none;
  stroke: var(--apple-secondary);
  stroke-width: 2;
  stroke-dasharray: 7 7;
  opacity: var(--melo-transfer-candidates, 0);
}

#step-5 .transfer-line-candidate-horizontal {
  stroke: var(--apple-blue);
}

#step-5 .transfer-line {
  opacity: 0;
  stroke-dashoffset: 0;
  transition: opacity 220ms ease;
}

#step-5 .transfer-point {
  opacity: 0;
  transform: scale(0.6);
  transition: opacity 220ms ease, transform 320ms var(--apple-ease);
}

#step-5 .transfer-stage.line-resolved .transfer-line {
  opacity: 1;
}

#step-5 .transfer-stage.line-resolved .transfer-line-candidate {
  opacity: 0;
}

#step-5 .transfer-stage.line-resolved.method-complete .transfer-point {
  opacity: 1;
  transform: scale(1);
}

#step-5 .transfer-stage[data-transfer-round="reverse-reading"].line-resolved .transfer-point {
  opacity: 1;
  transform: scale(1);
}

#step-5 .transfer-stage:not(.method-complete) .transfer-angle-map {
  opacity: 0;
}

.transfer-angle-ray {
  stroke: var(--apple-orange);
  stroke-width: 2.5;
  opacity: 0;
  transition: opacity 180ms ease;
}

.transfer-probe-reference {
  opacity: 0;
  transition: opacity 180ms ease;
}

.transfer-probe-anchor,
.transfer-probe-offset,
.transfer-reference-offset {
  fill: none;
  vector-effect: non-scaling-stroke;
}

.transfer-probe-anchor {
  stroke: #f5f5f766;
  stroke-width: 2;
  stroke-dasharray: 5 5;
}

.transfer-probe-offset,
.transfer-reference-offset {
  stroke: var(--apple-orange, #ff9f0a);
  stroke-width: 3;
  stroke-linecap: round;
}

.transfer-reference-offset {
  stroke-dasharray: 1;
  stroke-dashoffset: calc(1 - var(--melo-transfer-half-reference, 0));
}

.transfer-bridge-full .transfer-reference-offset {
  stroke-dashoffset: calc(1 - var(--melo-transfer-full-reference, 0));
}

.transfer-probe-point {
  fill: var(--apple-orange);
  opacity: 0;
  transition: opacity 180ms ease;
}

#step-5 .transfer-stage.has-probe .transfer-angle-ray,
#step-5 .transfer-stage.has-probe .transfer-probe-point,
#step-5 .transfer-stage.has-probe .transfer-probe-reference {
  opacity: 1;
}

.transfer-axis-label {
  position: absolute;
  z-index: 4;
  color: var(--apple-secondary);
  font-size: 0.72rem;
  opacity: var(--melo-transfer-coordinate, 0);
  pointer-events: none;
}

.transfer-axis-label-x {
  top: 52%;
  right: 5%;
}

.transfer-axis-label-y {
  top: 19%;
  left: 52%;
  color: var(--apple-blue);
}

.transfer-line-choices {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.65rem;
}

.transfer-line-choices .choice-button {
  display: grid;
  min-height: 4.6rem;
  grid-template-columns: 1.5rem minmax(0, 1fr);
  grid-template-rows: auto auto;
  align-items: center;
  gap: 0.08rem 0.55rem;
  text-align: left;
}

.transfer-line-choices .choice-button > span:nth-child(2) {
  font-weight: 650;
}

.transfer-line-choices .choice-button small {
  grid-column: 2;
  color: var(--apple-secondary);
}

.line-choice-icon {
  position: relative;
  grid-row: 1 / span 2;
  width: 1.4rem;
  height: 1.4rem;
}

.line-choice-icon::before {
  position: absolute;
  top: 50%;
  left: 50%;
  width: 1.25rem;
  height: 2px;
  border-radius: 2px;
  background: currentColor;
  content: "";
  transform: translate(-50%, -50%);
}

.line-choice-icon-vertical::before {
  transform: translate(-50%, -50%) rotate(90deg);
}

.line-choice-icon-horizontal {
  color: var(--apple-blue);
}

.transfer-method-builder {
  display: grid;
  gap: 0.85rem;
  padding: 0.95rem 0;
  border-top: 1px solid var(--apple-separator);
  border-bottom: 1px solid var(--apple-separator);
}

.transfer-method-builder[hidden] {
  display: none;
}

.transfer-method-head {
  display: grid;
  gap: 0.6rem;
}

.transfer-method-head > div:first-child {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 0.75rem;
}

.transfer-method-head strong {
  color: var(--apple-label);
  font-size: 0.92rem;
}

.transfer-method-head span,
.transfer-method-summary p {
  color: var(--apple-secondary);
  font-size: 0.78rem;
}

.transfer-method-progress {
  display: grid;
  grid-template-columns: repeat(var(--method-step-count, 3), minmax(0, 1fr));
  gap: 0.35rem;
}

.transfer-method-progress span {
  display: flex;
  min-width: 0;
  min-height: 1.75rem;
  align-items: center;
  justify-content: center;
  padding: 0.25rem 0.4rem;
  border-radius: 999px;
  background: var(--apple-surface);
  color: var(--apple-tertiary);
  font-size: 0.7rem;
  font-weight: 600;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
  transition: background-color 220ms ease, color 220ms ease, box-shadow 220ms ease;
}

.transfer-method-progress span.is-current {
  background: #2997ff18;
  color: var(--apple-blue);
  box-shadow: inset 0 0 0 1px #2997ff55;
}

.transfer-method-progress span.is-complete {
  background: #30d15817;
  color: var(--apple-green);
}

.transfer-method-step {
  display: grid;
  gap: 0.65rem;
}

.transfer-method-step[hidden] {
  display: none;
}

.transfer-method-step > p {
  margin: 0;
  color: var(--apple-label);
  font-size: 0.92rem;
  line-height: 1.45;
}

.transfer-method-choices {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.5rem;
}

.transfer-method-choices button {
  min-height: 2.75rem;
  padding: 0.55rem 0.75rem;
  border: 1px solid var(--apple-separator);
  border-radius: 12px;
  background: var(--apple-surface);
  color: var(--apple-label);
  cursor: pointer;
  font: inherit;
  font-size: 0.84rem;
  font-weight: 600;
  line-height: 1.25;
  transition: background-color 180ms ease, border-color 180ms ease, color 180ms ease, transform 180ms ease;
}

.transfer-method-choices button:hover:not(:disabled) {
  background: var(--apple-surface-raised);
}

.transfer-method-choices button:active:not(:disabled) {
  transform: scale(0.98);
}

.transfer-method-choices button.is-correct,
.transfer-method-choices button.is-selected {
  border-color: #30d15888;
  background: #30d15817;
  color: var(--apple-green);
}

.transfer-method-choices button.is-wrong {
  border-color: #ff453a88;
  background: #ff453a14;
  color: var(--apple-red);
}

.transfer-method-summary {
  display: grid;
  grid-template-columns: 1.75rem minmax(0, 1fr);
  gap: 0.55rem;
  align-items: center;
}

.transfer-method-summary[hidden] {
  display: none;
}

.transfer-method-summary > span {
  display: grid;
  width: 1.75rem;
  height: 1.75rem;
  place-items: center;
  border-radius: 50%;
  background: #30d1581f;
  color: var(--apple-green);
  font-weight: 700;
}

.transfer-method-summary p {
  margin: 0;
  line-height: 1.35;
}

.transfer-method-summary strong {
  color: var(--apple-label);
}

.transfer-angle-tool {
  padding-top: 0.9rem;
  border-top: 1px solid var(--apple-separator);
}

.transfer-tool-heading {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 0.75rem;
  margin-bottom: 0.65rem;
}

.transfer-tool-heading span,
.transfer-selection-count {
  color: var(--apple-secondary);
  font-size: 0.8rem;
}

.transfer-angle-grid {
  display: grid;
  grid-template-columns: repeat(5, minmax(0, 1fr));
  gap: 0.38rem;
}

.transfer-angle-grid button {
  display: grid;
  min-width: 0;
  min-height: 3.1rem;
  place-content: center;
  gap: 0.05rem;
  padding: 0.25rem;
  border: 0;
  border-radius: 10px;
  background: var(--apple-surface);
  color: var(--apple-label);
  cursor: pointer;
  transition: background-color 180ms ease, transform 180ms ease;
}

.transfer-angle-grid button:hover:not(:disabled) {
  background: var(--apple-surface-raised);
}

.transfer-angle-grid button:active:not(:disabled) {
  transform: scale(0.96);
}

.transfer-angle-grid button small {
  color: var(--apple-secondary);
  font-size: 0.68rem;
}

.transfer-angle-grid button.is-probing {
  box-shadow: inset 0 0 0 2px var(--apple-orange);
}

.transfer-angle-grid button.is-selected {
  background: #2997ff22;
  color: var(--apple-blue);
  box-shadow: inset 0 0 0 2px var(--apple-blue);
}

.transfer-angle-grid button.is-wrong {
  background: #ff453a18;
  box-shadow: inset 0 0 0 2px var(--apple-red);
}

.transfer-selection-count {
  margin: 0.55rem 0 0;
}

#step-5 .transfer-stage.transfer-resolved .melo-transfer-result {
  right: auto;
  left: 0.9rem;
  transform: translateY(-50%);
}

@media (max-width: 720px) {
  #step-3 .angle-stage[data-renderer="svg"] #angle-svg-fallback {
    width: min(calc(100% - 0.5rem), 28rem);
  }

  .angle-reading-layer {
    width: min(calc(100% - 0.5rem), 28rem);
  }

  #step-5 .transfer-stage {
    min-height: 30rem;
  }

  #step-5 .transfer-stage > #transfer-circle-map {
    transform: translateY(1.9rem) scale(0.72);
  }

  .transfer-axis-label-x {
    right: 2%;
  }

  .transfer-line-choices {
    grid-template-columns: 1fr;
  }

  .transfer-method-choices {
    grid-template-columns: 1fr;
  }

  .transfer-angle-grid {
    grid-template-columns: repeat(3, minmax(0, 1fr));
  }

  .transfer-angle-grid button {
    min-height: 3.25rem;
  }

  .solution-turn-runner {
    transform:
      translate(-50%, -50%)
      rotate(calc(-120deg + var(--melo-solution-turn, 0) * 360deg))
      translateX(min(8.1rem, 38vw));
  }
}

@media (prefers-reduced-motion: reduce) {
  .solution-turn-runner,
  .solution-turn-copy,
  #step-5 .transfer-line,
  #step-5 .transfer-point,
  .transfer-angle-ray,
  .transfer-probe-point,
  .transfer-angle-grid button {
    transition-duration: 180ms !important;
  }
}

/* Explicit lesson pages: wheel/touch scroll only the active page. Page
   changes are separate, reversible actions with directional continuity. */
.lesson-page-navigation {
  display: flex;
  align-items: center;
  gap: 0.35rem;
  pointer-events: none;
}

.lesson-page-button {
  display: grid;
  width: 2.75rem;
  height: 2.75rem;
  place-items: center;
  padding: 0;
  border: 0;
  border-radius: 50%;
  background: var(--apple-material, #1c1c1edb);
  box-shadow: inset 0 0 0 1px #ffffff12;
  color: var(--apple-label, #f5f5f7);
  cursor: pointer;
  font-size: 1.05rem;
  line-height: 1;
  pointer-events: auto;
  transition: background-color 160ms ease, color 160ms ease, opacity 160ms ease, transform 120ms ease;
  -webkit-backdrop-filter: saturate(145%) blur(22px);
  backdrop-filter: saturate(145%) blur(22px);
}

.lesson-page-button:hover:not(:disabled) {
  background: var(--apple-control-hover, #3a3a3c);
}

.lesson-page-button:active:not(:disabled) {
  transform: scale(0.94);
}

.lesson-page-button:disabled {
  opacity: 0.28;
}

.lesson-page-navigation .lesson-page-hint {
  min-height: 2.2rem;
  pointer-events: none;
}

/* Step 2: labels remain readable while their geometry moves. KaTeX stays
   unscaled inside the tag; degrees are a second, high-contrast unit. */
.intersection-angle-tag {
  min-width: 8.4rem;
  gap: 0.16rem 0.55rem;
  padding: 0.58rem 0.76rem;
  background: #1c1c1ef7;
  box-shadow: 0 6px 16px #000a, inset 0 0 0 1px #ffffff1f;
  transform: translateY(-50%) scale(1.08);
  transform-origin: left center;
}

.intersection-angle-tag strong {
  font-size: 1.12rem;
  line-height: 1.15;
}

.intersection-angle-tag > span {
  font-size: 0.92rem;
  line-height: 1.15;
}

.intersection-angle-tag .katex,
.intersection-coordinate-tag .katex {
  font-size: 1em;
}

.intersection-coordinate-tag {
  min-width: 8.4rem;
  padding: 0.52rem 0.68rem 0.56rem 0.8rem;
  background: #1c1c1ef7;
  box-shadow: 0 6px 16px #000a, inset 0 0 0 1px #ffffff1f;
}

.intersection-coordinate-tag small {
  font-size: 0.65rem;
}

.intersection-coordinate-tag strong {
  font-size: 0.96rem;
}

.intersection-annotation-layer.labels-on-left .intersection-angle-tag {
  transform: translate(-100%, -50%) scale(1.08);
  transform-origin: right center;
}

/* Step 3: the conversion is a recoverable unit transformation, not a table
   of unrelated pairs. */
.radian-bridge {
  display: grid;
  gap: 0.55rem;
  margin-top: 1.25rem;
  padding: 0.9rem;
  border-radius: 14px;
  background: var(--apple-surface, #1c1c1e);
  box-shadow: inset 0 0 0 1px #ffffff12;
}

.radian-anchor,
.radian-one {
  display: flex;
  min-width: 0;
  align-items: center;
  justify-content: space-between;
  gap: 0.75rem;
  padding: 0.65rem 0.75rem;
  border-radius: 11px;
  background: #242426;
}

.radian-anchor small,
.radian-one small {
  color: var(--apple-secondary, #aeaeb2);
}

.radian-anchor strong,
.radian-one strong {
  color: var(--apple-blue, #2997ff);
  font-size: 1rem;
  text-align: right;
}

.radian-conversion {
  display: grid;
  min-width: 0;
  grid-template-columns: minmax(0, 1fr) auto auto;
  gap: 0.55rem;
  align-items: center;
  padding: 0.7rem 0.75rem;
  border-radius: 11px;
  background: #121214;
  color: var(--apple-secondary, #aeaeb2);
}

.radian-conversion > span:first-child {
  min-width: 0;
  overflow-x: auto;
  scrollbar-width: none;
}

.radian-conversion strong {
  color: var(--apple-label, #f5f5f7);
}

.radian-recovery {
  margin: 0.1rem 0 0 !important;
  color: var(--apple-secondary, #aeaeb2) !important;
  font-size: 0.82rem !important;
}

/* Step 4: make the full-turn animation impossible to miss and keep its path
   physically attached to the same circle. */
.solution-turn-orbit {
  position: absolute;
  z-index: 4;
  inset: 6%;
  border: 1px solid #ff9f0a66;
  border-radius: 50%;
  opacity: calc(var(--melo-solution-turn, 0) * 0.9);
  pointer-events: none;
  transform: scale(calc(0.94 + var(--melo-solution-turn, 0) * 0.06));
}

.solution-turn-runner {
  width: 1.05rem;
  height: 1.05rem;
  background: #ff9f0a;
  box-shadow: 0 0 0 0.32rem #ff9f0a2e, 0 0 1.25rem #ff9f0a8c;
  will-change: transform, opacity;
}

/* Step 5: remove the decorative empty oval and make the circle itself the
   reference map. */
#step-5 .melo-motion-stage::before {
  display: none;
}

.transfer-angle-map .transfer-angle-tick {
  stroke: #8e8e93;
  stroke-width: 1.4;
  transition: stroke 160ms ease;
}

.transfer-angle-map {
  opacity: var(--melo-transfer-base, 0);
}

.transfer-angle-map .transfer-angle-label {
  fill: #d1d1d6;
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", "Segoe UI", system-ui, sans-serif;
  font-size: 10px;
  font-variant-numeric: tabular-nums;
  font-weight: 650;
  paint-order: stroke;
  stroke: #050506;
  stroke-width: 3px;
  stroke-linejoin: round;
  text-anchor: middle;
  transition: fill 160ms ease, font-size 160ms ease;
}

.transfer-angle-map [data-map-angle].is-probing .transfer-angle-tick {
  stroke: var(--apple-orange, #ff9f0a);
  stroke-width: 3;
}

.transfer-angle-map [data-map-angle].is-probing .transfer-angle-label {
  fill: var(--apple-orange, #ff9f0a);
  font-size: 12px;
}

.transfer-angle-map [data-map-angle].is-selected .transfer-angle-tick,
.transfer-angle-map [data-map-angle].is-selected .transfer-angle-label {
  stroke: var(--apple-blue, #2997ff);
  fill: var(--apple-blue, #2997ff);
}

.transfer-probe-readout {
  position: absolute;
  z-index: 6;
  bottom: 0.8rem;
  left: 50%;
  display: grid;
  width: min(calc(100% - 2rem), 22rem);
  justify-items: center;
  gap: 0.08rem;
  padding: 0.55rem 0.75rem;
  border-radius: 12px;
  background: #1c1c1ef2;
  box-shadow: 0 6px 16px #0009, inset 0 0 0 1px #ffffff14;
  color: var(--apple-label, #f5f5f7);
  pointer-events: none;
  transform: translateX(-50%);
  -webkit-backdrop-filter: blur(18px);
  backdrop-filter: blur(18px);
}

.transfer-probe-readout strong {
  color: var(--apple-orange, #ff9f0a);
}

.transfer-probe-readout span {
  color: var(--apple-secondary, #aeaeb2);
  font-size: 0.78rem;
}

.transfer-probe-readout .transfer-probe-reference-copy {
  color: var(--apple-orange, #ff9f0a);
  font-weight: 700;
}

.angle-memory-pattern {
  min-width: 0;
  margin-top: 0.75rem;
  padding: 0.75rem;
  overflow-x: hidden;
  border-radius: 12px;
  background: #121214;
  box-shadow: inset 0 0 0 1px #ffffff0d;
}

.angle-memory-pattern > p {
  min-width: 0;
  margin: 0 0 0.55rem;
  color: var(--apple-secondary, #aeaeb2);
  font-size: 0.78rem;
}

.angle-memory-pattern > p strong {
  color: var(--apple-label, #f5f5f7);
}

.angle-pattern-row {
  display: grid;
  min-width: 0;
  grid-template-columns: 3.2rem repeat(5, minmax(0, 1fr));
  align-items: center;
  border-top: 1px solid #ffffff0d;
  color: var(--apple-label, #f5f5f7);
  font-size: 0.76rem;
  text-align: center;
}

#step-5 .transfer-copy,
#step-5 .transfer-angle-tool,
#step-5 .transfer-angle-grid {
  min-width: 0;
  width: 100%;
}

.angle-pattern-row > * {
  padding: 0.4rem 0.2rem;
}

.angle-pattern-row small {
  color: var(--apple-secondary, #aeaeb2);
  text-align: left;
}

.angle-pattern-row--cos span {
  color: var(--apple-blue, #2997ff);
}

.angle-pattern-row--sin span {
  color: var(--apple-orange, #ff9f0a);
}

.angle-memory-pattern .angle-pattern-rule {
  margin-top: 0.55rem;
}

@media (max-width: 720px) {
  .lesson-page-chrome {
    right: max(0.65rem, env(safe-area-inset-right));
    left: max(0.65rem, env(safe-area-inset-left));
    gap: 0.45rem;
  }

  .lesson-page-navigation {
    gap: 0.22rem;
  }

  .lesson-page-navigation .lesson-page-hint {
    max-width: 11.5rem;
    padding-inline: 0.5rem;
    font-size: 0.64rem;
  }

  .lesson-page-button {
    width: 2.6rem;
    height: 2.6rem;
  }

  .intersection-angle-tag {
    min-width: 7.7rem;
    padding: 0.52rem 0.64rem;
  }

  .intersection-angle-tag strong {
    font-size: 1.02rem;
  }

  .intersection-angle-tag > span {
    font-size: 0.88rem;
  }

  .radian-anchor,
  .radian-one {
    align-items: flex-start;
    flex-direction: column;
    gap: 0.2rem;
  }

  .radian-anchor strong,
  .radian-one strong {
    text-align: left;
  }

  .radian-conversion {
    grid-template-columns: 1fr auto;
  }

  .radian-conversion > span:first-child {
    grid-column: 1 / -1;
  }

  #step-5 .transfer-stage > #transfer-circle-map {
    transform: translateY(1.3rem) scale(0.76);
  }

  .transfer-probe-readout {
    bottom: 0.55rem;
    width: calc(100% - 1rem);
  }

  .angle-memory-pattern {
    padding-inline: 0.55rem;
  }

  .angle-pattern-row {
    grid-template-columns: 2.55rem repeat(5, minmax(0, 1fr));
    font-size: 0.64rem;
  }

  .angle-pattern-row > * {
    min-width: 0;
    padding-inline: 0.08rem;
  }

  .angle-pattern-row .katex {
    font-size: 0.88em;
  }
}

@media (prefers-reduced-motion: reduce) {
  .lesson-page-button,
  .solution-turn-orbit,
  .transfer-angle-map * {
    transition-duration: 160ms !important;
  }
}

/* Step 5 continuous camera: one unit circle is never replaced by a cropped
   drawing. The camera moves full circle -> first quadrant -> half -> full,
   while speech focus is expressed on the referenced mathematical object. */
#memory-circle-map,
#transfer-circle-map {
  overflow: hidden;
}

.memory-quadrant {
  top: 3.35rem;
  width: min(calc(100% - 1rem), 30rem);
  contain: layout paint;
  transition: top 600ms var(--melo-morph, cubic-bezier(.22, 1, .36, 1));
}

.angle-memory-stage[data-visual-attention^="foundation"] .memory-quadrant {
  top: 0.4rem;
}

#step-5 .transfer-stage > #transfer-circle-map {
  width: min(calc(100% - 1rem), 30rem);
  max-width: none;
  overflow: hidden;
  transform: translateY(1.7rem);
  transform-origin: 50% 50%;
}

.memory-axis,
.memory-quarter-arc,
.memory-foundation-origin,
.memory-foundation-units,
.memory-foundation-cardinals,
.memory-turn-track,
.memory-turn-progress,
.memory-turn-point,
.memory-repeat-proof,
.memory-rays,
.memory-projection-guides,
.memory-sweep-point,
.memory-axis-caption,
.memory-coordinate-pair,
.memory-angle-label,
.memory-value-token,
.memory-general-template,
#transfer-circle-map .transfer-axis,
#transfer-circle-map .transfer-circle,
#transfer-circle-map .transfer-bridge-half,
#transfer-circle-map .transfer-bridge-full,
#transfer-circle-map .transfer-sign-guide,
#step-5 .transfer-brief {
  transition:
    opacity 220ms ease,
    filter 260ms ease,
    transform 420ms var(--melo-morph, cubic-bezier(.22, 1, .36, 1)),
    color 220ms ease;
}

.angle-memory-stage[data-visual-attention] .memory-axis,
.angle-memory-stage[data-visual-attention] .memory-quarter-arc,
.angle-memory-stage[data-visual-attention] .memory-foundation-origin,
.angle-memory-stage[data-visual-attention] .memory-foundation-units,
.angle-memory-stage[data-visual-attention] .memory-foundation-cardinals,
.angle-memory-stage[data-visual-attention] .memory-turn-track,
.angle-memory-stage[data-visual-attention] .memory-turn-progress,
.angle-memory-stage[data-visual-attention] .memory-turn-point,
.angle-memory-stage[data-visual-attention] .memory-repeat-proof,
.angle-memory-stage[data-visual-attention] .memory-rays,
.angle-memory-stage[data-visual-attention] .memory-projection-guides,
.angle-memory-stage[data-visual-attention] .memory-sweep-point,
.angle-memory-stage[data-visual-attention] .memory-axis-caption,
.angle-memory-stage[data-visual-attention] .memory-coordinate-pair,
.angle-memory-stage[data-visual-attention] .memory-angle-label,
.angle-memory-stage[data-visual-attention] .memory-value-token,
.angle-memory-stage[data-visual-attention] .memory-general-template {
  filter: saturate(0.72) brightness(0.72);
}

.angle-memory-stage[data-visual-attention="foundation-origin"] .memory-axis,
.angle-memory-stage[data-visual-attention="foundation-origin"] .memory-foundation-origin,
.angle-memory-stage[data-visual-attention="foundation-units"] .memory-quarter-arc,
.angle-memory-stage[data-visual-attention="foundation-units"] .memory-foundation-units,
.angle-memory-stage[data-visual-attention="foundation-turn"] .memory-turn-track,
.angle-memory-stage[data-visual-attention="foundation-turn"] .memory-turn-progress,
.angle-memory-stage[data-visual-attention="foundation-turn"] .memory-turn-point,
.angle-memory-stage[data-visual-attention="foundation-turn"] .memory-foundation-cardinals,
.angle-memory-stage[data-visual-attention="foundation-repeat"] .memory-repeat-proof,
.angle-memory-stage[data-visual-attention="foundation-repeat"] .memory-foundation-units,
.angle-memory-stage[data-visual-attention="full-circle"] .memory-quarter-arc,
.angle-memory-stage[data-visual-attention="circle-camera"] .memory-quarter-arc,
.angle-memory-stage[data-visual-attention="circle-camera"] .memory-axis,
.angle-memory-stage[data-visual-attention="angles"] .memory-rays,
.angle-memory-stage[data-visual-attention="angles"] .memory-angle-label,
.angle-memory-stage[data-visual-attention="counts"] .memory-value-token,
.angle-memory-stage[data-visual-attention="roots"] .memory-value-token,
.angle-memory-stage[data-visual-attention="denominators"] .memory-value-token,
.angle-memory-stage[data-visual-attention="template"] .memory-value-token,
.angle-memory-stage[data-visual-attention="template"] .memory-general-template,
.angle-memory-stage[data-visual-attention="simplify"] .memory-value-token,
.angle-memory-stage[data-visual-attention="cos-projection"] .memory-projection-guides,
.angle-memory-stage[data-visual-attention="cos-projection"] .memory-sweep-point,
.angle-memory-stage[data-visual-attention="cos-projection"] .memory-axis-caption-x,
.angle-memory-stage[data-visual-attention="cos-projection"] .memory-coordinate-pair,
.angle-memory-stage[data-visual-attention="sin-projection"] .memory-projection-guides,
.angle-memory-stage[data-visual-attention="sin-projection"] .memory-sweep-point,
.angle-memory-stage[data-visual-attention="sin-projection"] .memory-axis-caption-y,
.angle-memory-stage[data-visual-attention="sin-projection"] .memory-coordinate-pair,
.angle-memory-stage[data-visual-attention="sixty"] .memory-angle-label-60,
.angle-memory-stage[data-visual-attention="sixty"] [data-pattern-slot="1"],
.angle-memory-stage[data-visual-attention="sixty"] [data-pattern-slot="3"] {
  filter: saturate(1.15) brightness(1.22) drop-shadow(0 0 7px #2997ff66);
}

.angle-memory-stage[data-visual-attention="roots"] .memory-token-radical,
.angle-memory-stage[data-visual-attention="denominators"] .memory-token-bar,
.angle-memory-stage[data-visual-attention="denominators"] .memory-token-denominator {
  color: var(--apple-orange, #ff9f0a);
}

.angle-memory-stage[data-visual-attention="template"] .memory-token-number {
  color: var(--apple-orange, #ff9f0a);
}

.transfer-reference-line,
.transfer-reference-ray {
  fill: none;
  vector-effect: non-scaling-stroke;
}

.transfer-reference-line {
  stroke: var(--apple-orange, #ff9f0a);
  stroke-width: 2.5;
  stroke-dasharray: 1;
  stroke-dashoffset: calc(1 - var(--melo-transfer-half-line, 0));
}

.transfer-reference-ray {
  stroke: #f5f5f7;
  stroke-width: 2;
  stroke-linecap: round;
}

.transfer-reference-point {
  fill: #f5f5f7;
  transform-box: fill-box;
  transform-origin: center;
}

.transfer-bridge-half .transfer-reference-point {
  transform: scale(var(--melo-transfer-half-reference, 0));
}

.transfer-bridge-full .transfer-reference-point {
  transform: scale(var(--melo-transfer-full-reference, 0));
}

.transfer-bridge-half .transfer-anchor-label { opacity: var(--melo-transfer-half-anchor, 0); }
.transfer-bridge-half .transfer-reference-ray-a,
.transfer-bridge-half .transfer-reference-point-a,
.transfer-bridge-half .transfer-reference-label-a,
.transfer-bridge-half .transfer-reference-offset-a,
.transfer-bridge-half .transfer-reference-equation-a { opacity: var(--melo-transfer-half-right, 0); }
.transfer-bridge-half .transfer-reference-ray-b,
.transfer-bridge-half .transfer-reference-point-b,
.transfer-bridge-half .transfer-reference-label-b,
.transfer-bridge-half .transfer-reference-offset-b,
.transfer-bridge-half .transfer-reference-equation-b { opacity: var(--melo-transfer-half-left, 0); }

.transfer-bridge-full .transfer-reference-ray-a,
.transfer-bridge-full .transfer-reference-point-a,
.transfer-bridge-full .transfer-reference-label-a { opacity: var(--melo-transfer-full-known, 0); }
.transfer-bridge-full .transfer-reference-ray-b,
.transfer-bridge-full .transfer-reference-point-b,
.transfer-bridge-full .transfer-reference-label-b,
.transfer-bridge-full .transfer-reference-offset-b,
.transfer-bridge-full .transfer-reference-equation-b { opacity: var(--melo-transfer-full-left, 0); }
.transfer-bridge-full .transfer-reference-ray-c,
.transfer-bridge-full .transfer-reference-point-c,
.transfer-bridge-full .transfer-reference-label-c,
.transfer-bridge-full .transfer-reference-offset-c,
.transfer-bridge-full .transfer-reference-equation-c { opacity: var(--melo-transfer-full-right, 0); }

.transfer-reference-label,
.transfer-sign-label {
  fill: #f5f5f7;
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", "Segoe UI", system-ui, sans-serif;
  font-size: 12px;
  font-weight: 700;
  text-anchor: middle;
}

.transfer-reference-label-b {
  text-anchor: start;
}

.transfer-reference-label-a {
  text-anchor: end;
}

.transfer-reference-label-y {
  fill: var(--apple-orange, #ff9f0a);
  font-size: 10px;
}

.transfer-anchor-label,
.transfer-reference-equation {
  fill: #aeaeb2;
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", "Segoe UI", system-ui, sans-serif;
  font-size: 10px;
  font-weight: 700;
  text-anchor: middle;
}

.transfer-reference-equation {
  fill: var(--apple-orange, #ff9f0a);
  font-size: 9px;
}

.transfer-reference-line-negative {
  stroke-dasharray: 1;
  stroke-dashoffset: calc(1 - var(--melo-transfer-full-line, 0));
  opacity: var(--melo-transfer-full-line, 0);
}

.transfer-bridge-half {
  opacity: var(--melo-transfer-half-reference, 0);
}

.transfer-bridge-full {
  opacity: var(--melo-transfer-full-reference, 0);
}

.transfer-sign-guide {
  opacity: max(var(--melo-transfer-sign-guide, 0), var(--melo-transfer-negative-cue, 0));
}

.transfer-sign-label {
  fill: var(--apple-secondary, #a1a1a8);
  font-size: 10px;
  opacity: var(--melo-transfer-sign-guide, 0);
}

.transfer-sign-y-negative {
  opacity: max(var(--melo-transfer-sign-guide, 0), var(--melo-transfer-negative-cue, 0));
}

/* These annotations explain the full-circle construction. Keep them readable
   on the narrow stage without moving any point, ray or angle. */
.transfer-bridge-full .transfer-reference-label,
.transfer-stage[data-melo-clip="full-circle-bridge"] .transfer-sign-label {
  font-size: 14px;
}

#step-5 .transfer-stage[data-visual-attention] #transfer-circle-map > :not(.transfer-bridge-half, .transfer-bridge-full, .transfer-sign-guide) {
  transition: opacity 220ms ease, filter 260ms ease;
}

#step-5 .transfer-stage[data-visual-attention="half-rays"] #transfer-circle-map > :not(.transfer-bridge-half, .transfer-bridge-full, .transfer-sign-guide),
#step-5 .transfer-stage[data-visual-attention="half-height"] #transfer-circle-map > :not(.transfer-bridge-half, .transfer-bridge-full, .transfer-sign-guide),
#step-5 .transfer-stage[data-visual-attention="full-reference"] #transfer-circle-map > :not(.transfer-bridge-half, .transfer-bridge-full, .transfer-sign-guide),
#step-5 .transfer-stage[data-visual-attention="sign-guide"] #transfer-circle-map > :not(.transfer-bridge-half, .transfer-bridge-full, .transfer-sign-guide) {
  filter: saturate(0.7) brightness(0.44);
}

#step-5 .transfer-stage[data-visual-attention="half-rays"] .transfer-bridge-half,
#step-5 .transfer-stage[data-visual-attention="half-height"] .transfer-bridge-half,
#step-5 .transfer-stage[data-visual-attention="full-reference"] .transfer-bridge-full,
#step-5 .transfer-stage[data-visual-attention="sign-guide"] .transfer-sign-guide {
  opacity: 1;
  filter: drop-shadow(0 0 8px #2997ff45);
}

#step-5 .transfer-stage[data-visual-attention="transfer-equation"] #transfer-circle-map,
#step-5 .transfer-stage[data-visual-attention="line-choice"] #transfer-circle-map {
  opacity: 0.42;
}

#step-5 .transfer-stage[data-visual-attention="transfer-equation"] .transfer-brief,
#step-5 .transfer-stage[data-visual-attention="line-choice"] .transfer-line-candidate {
  filter: brightness(1.18) drop-shadow(0 0 8px #2997ff55);
}

#step-5 .transfer-stage.is-circle-bridge .transfer-angle-map,
#step-5 .transfer-stage.is-circle-bridge .transfer-line-candidate,
#step-5 .transfer-stage.is-circle-bridge .transfer-line,
#step-5 .transfer-stage.is-circle-bridge .transfer-probe-reference,
#step-5 .transfer-stage.is-circle-bridge .transfer-angle-ray,
#step-5 .transfer-stage.is-circle-bridge .transfer-probe-point,
#step-5 .transfer-stage.is-circle-bridge .transfer-point {
  opacity: 0 !important;
}

#step-5 .transfer-stage.is-narrating[data-melo-clip="full-circle-bridge"] .transfer-angle-map,
#step-5 .transfer-stage.is-narrating[data-melo-clip="transfer"] .transfer-angle-map,
#step-5 .transfer-stage.is-narrating[data-melo-clip="full-circle-bridge"] .transfer-line-candidate,
#step-5 .transfer-stage.is-narrating[data-melo-clip="full-circle-bridge"] .transfer-line,
#step-5 .transfer-stage.is-narrating[data-melo-clip="full-circle-bridge"] .transfer-probe-reference,
#step-5 .transfer-stage.is-narrating[data-melo-clip="full-circle-bridge"] .transfer-angle-ray,
#step-5 .transfer-stage.is-narrating[data-melo-clip="full-circle-bridge"] .transfer-probe-point,
#step-5 .transfer-stage.is-narrating[data-melo-clip="full-circle-bridge"] .transfer-point {
  opacity: 0 !important;
  visibility: hidden;
}

@media (max-width: 720px) {
  .memory-quadrant {
    top: 3.7rem;
    width: min(calc(100% - 0.5rem), 27rem);
  }

  #step-5 .transfer-stage > #transfer-circle-map {
    width: min(calc(100% - 0.4rem), 27rem);
    transform: translateY(1.55rem);
  }

  #step-5 .transfer-stage:not(.is-memory-mode) {
    min-height: 22rem;
    padding-top: 4.6rem;
  }

  #step-5 .transfer-stage:not(.is-memory-mode) > #transfer-circle-map {
    width: min(calc(100% - 0.4rem), 20.5rem);
    transform: translateY(0.45rem);
  }

  #step-5 .transfer-stage.is-circle-bridge {
    min-height: 27rem;
  }

  #step-5 .transfer-stage.is-circle-bridge > #transfer-circle-map {
    width: min(calc(100% - 0.4rem), 25rem);
  }
}

/* Visual derivation contract: every spoken degree→radian claim changes the
   same persistent object. Nothing here is a decorative card slideshow. */
.radian-derivation-visual {
  position: absolute;
  z-index: 12;
  inset: 0.75rem;
  display: grid;
  min-width: 0;
  grid-template-rows: minmax(7.2rem, 1fr) auto auto auto auto;
  align-content: center;
  gap: 0.55rem;
  padding: clamp(0.8rem, 2vw, 1.2rem);
  overflow: hidden;
  border-radius: 14px;
  background: #0c0c0e;
  box-shadow: inset 0 0 0 1px #ffffff12;
  opacity: var(--melo-radian-machine, 0);
  transform: translateY(calc((1 - var(--melo-radian-machine, 0)) * 0.6rem));
}

.radian-visual-orbit {
  position: relative;
  width: min(100%, 24rem);
  min-height: 7.2rem;
  justify-self: center;
}

.radian-visual-orbit svg {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
}

.radian-orbit-muted,
.radian-orbit-progress {
  fill: none;
  stroke-linecap: round;
  stroke-width: 4;
}

.radian-orbit-muted {
  stroke: #ffffff14;
}

.radian-orbit-progress {
  stroke: var(--apple-blue, #2997ff);
  stroke-dasharray: 1;
  stroke-dashoffset: calc(1 - var(--melo-radian-half-turn, 0));
  filter: drop-shadow(0 0 0.45rem #2997ff73);
}

.radian-orbit-start {
  fill: var(--apple-orange, #ff9f0a);
  opacity: var(--melo-radian-half-turn, 0);
}

.radian-orbit-runner {
  fill: #ffffff;
  opacity: var(--melo-radian-half-turn, 0);
}

.radian-orbit-degree,
.radian-orbit-equals,
.radian-orbit-radian {
  position: absolute;
  bottom: 0.2rem;
  opacity: var(--melo-radian-equivalence, 0);
  transform: translateY(calc((1 - var(--melo-radian-equivalence, 0)) * 0.4rem));
}

.radian-orbit-degree {
  left: 6%;
  color: var(--apple-label, #f5f5f7);
}

.radian-orbit-equals {
  left: 50%;
  color: var(--apple-tertiary, #8e8e93);
  font-weight: 700;
  transform: translate(-50%, calc((1 - var(--melo-radian-equivalence, 0)) * 0.4rem));
}

.radian-orbit-radian {
  right: 6%;
  color: var(--apple-blue, #2997ff);
}

.radian-identity-visual {
  display: grid;
  width: min(100%, 25rem);
  min-width: 0;
  grid-template-columns: auto auto minmax(0, auto);
  align-items: center;
  justify-content: center;
  gap: 0.65rem;
  justify-self: center;
  color: var(--apple-label, #f5f5f7);
  opacity: var(--melo-radian-ratio, 0);
  transform: translateY(calc((1 - var(--melo-radian-ratio, 0)) * 0.45rem));
}

.radian-identity-one,
.radian-identity-equals {
  font-size: 1.15rem;
  font-weight: 700;
}

.radian-identity-fraction {
  color: var(--apple-blue, #2997ff);
  font-size: clamp(1.05rem, 3vw, 1.35rem);
}

.radian-identity-visual small {
  grid-column: 1 / -1;
  color: var(--apple-secondary, #aeaeb2);
  font-size: 0.68rem;
  letter-spacing: 0.01em;
  text-align: center;
}

.radian-pipeline {
  display: grid;
  min-width: 0;
  grid-template-columns: minmax(0, 1fr) auto;
  align-items: center;
  gap: 0.7rem;
  opacity: var(--melo-radian-sixty, 0);
  transform: translateY(calc((1 - var(--melo-radian-sixty, 0)) * 0.5rem));
}

.radian-pipeline-expression {
  display: flex;
  min-width: 0;
  align-items: center;
  justify-content: center;
  gap: clamp(0.35rem, 1.5vw, 0.65rem);
  color: var(--apple-label, #f5f5f7);
  font-size: clamp(1rem, 3vw, 1.32rem);
  white-space: nowrap;
}

.radian-live-fraction {
  display: inline-grid;
  grid-template-rows: auto 1px auto;
  align-items: center;
  text-align: center;
}

.radian-live-fraction::before {
  grid-row: 2;
  width: 100%;
  height: 1px;
  background: currentColor;
  content: "";
}

.radian-live-numerator {
  grid-row: 1;
  padding: 0 0.2rem 0.14rem;
}

.radian-live-denominator {
  grid-row: 3;
  padding: 0.14rem 0.2rem 0;
}

.radian-degree-token {
  position: relative;
  display: inline-block;
  color: var(--apple-orange, #ff9f0a);
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", system-ui, sans-serif;
  font-size: 0.85em;
  font-style: normal;
  font-weight: 700;
}

.radian-degree-token::after {
  position: absolute;
  top: 50%;
  left: -0.18em;
  width: 1.35em;
  height: 2px;
  border-radius: 2px;
  background: var(--apple-red, #ff453a);
  content: "";
  opacity: var(--melo-radian-cancel, 0);
  transform: rotate(-45deg) scaleX(var(--melo-radian-cancel, 0));
}

.radian-pipeline-arrow {
  color: var(--apple-tertiary, #8e8e93);
  opacity: var(--melo-radian-sixty-result, 0);
}

.radian-pipeline-result {
  color: var(--apple-green, #30d158);
  font-weight: 700;
  opacity: var(--melo-radian-sixty-result, 0);
  transform: translateX(calc((1 - var(--melo-radian-sixty-result, 0)) * -0.35rem));
}

.radian-same-angle {
  position: relative;
  display: grid;
  min-width: 7rem;
  grid-template-columns: auto auto auto;
  align-items: center;
  gap: 0.3rem;
  opacity: var(--melo-radian-language, 0);
}

.radian-same-angle svg {
  grid-column: 1 / -1;
  width: 3.8rem;
  justify-self: center;
}

.radian-same-angle circle {
  fill: none;
  stroke: #ffffff24;
}

.radian-same-angle path {
  fill: #2997ff24;
  stroke: var(--apple-blue, #2997ff);
}

.radian-language-before {
  color: var(--apple-orange, #ff9f0a);
}

.radian-language-after {
  grid-column: 3;
  grid-row: 2;
  color: var(--apple-blue, #2997ff);
  opacity: var(--melo-radian-sixty-result, 0);
}

.radian-language-question {
  grid-column: 3;
  grid-row: 2;
  color: var(--apple-secondary, #aeaeb2);
  opacity: calc(1 - var(--melo-radian-sixty-result, 0));
}

.radian-same-angle small {
  grid-column: 1 / -1;
  color: var(--apple-secondary, #aeaeb2);
  font-size: 0.62rem;
  text-align: center;
}

.radian-transfer-row {
  display: grid;
  min-width: 0;
  grid-template-columns: minmax(0, 1fr) auto minmax(0, 0.65fr);
  align-items: center;
  gap: 0.55rem;
  padding-top: 0.45rem;
  border-top: 1px solid #ffffff12;
  color: var(--apple-secondary, #aeaeb2);
  font-size: clamp(0.78rem, 2.4vw, 1rem);
}

.radian-transfer-row strong {
  color: var(--apple-blue, #2997ff);
  text-align: right;
}

.radian-transfer-top {
  opacity: var(--melo-radian-top-result, 0);
  transform: translateX(calc((1 - var(--melo-radian-top-result, 0)) * -0.55rem));
}

.radian-transfer-bottom {
  opacity: var(--melo-radian-bottom-result, 0);
  transform: translateX(calc((1 - var(--melo-radian-bottom-result, 0)) * -0.55rem));
}

.radian-recovery-chain {
  display: grid;
  grid-template-columns: 1fr auto 1fr auto 1fr auto 1fr;
  align-items: center;
  gap: 0.3rem;
  padding: 0.6rem;
  border-radius: 12px;
  background: #1c1c1e;
  box-shadow: inset 0 0 0 1px #ffffff12;
  opacity: var(--melo-radian-recovery, 0);
  transform: translateY(calc((1 - var(--melo-radian-recovery, 0)) * 0.45rem));
}

.radian-recovery-chain > span {
  display: grid;
  min-width: 0;
  justify-items: center;
  gap: 0.14rem;
}

.radian-recovery-chain b {
  color: var(--apple-blue, #2997ff);
  font-size: 1.05rem;
}

.radian-recovery-chain small {
  color: var(--apple-secondary, #aeaeb2);
  font-size: 0.58rem;
  text-align: center;
}

.radian-recovery-chain > i {
  color: var(--apple-tertiary, #8e8e93);
  font-style: normal;
}

.radian-recall-builder {
  gap: 0.9rem;
  padding: 1rem;
}

.radian-builder-heading {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr) auto;
  align-items: center;
  gap: 0.7rem;
}

.radian-builder-heading > span:nth-child(2) {
  display: grid;
  gap: 0.08rem;
}

.radian-builder-heading small,
.radian-builder-result small {
  color: var(--apple-secondary, #aeaeb2);
}

.radian-builder-icon {
  display: grid;
  width: 2.35rem;
  height: 2.35rem;
  place-items: center;
  border-radius: 50%;
  background: #2997ff1f;
  color: var(--apple-blue, #2997ff);
  font-size: 1.25rem;
}

.radian-builder-anchor {
  color: var(--apple-blue, #2997ff);
  font-size: 0.92rem;
}

.radian-builder-step {
  min-width: 0;
  margin: 0;
  padding: 0.75rem 0 0;
  border: 0;
  border-top: 1px solid #ffffff12;
}

.radian-builder-step legend {
  width: 100%;
  padding: 0 0 0.65rem;
  color: var(--apple-label, #f5f5f7);
  font-size: 0.88rem;
  line-height: 1.42;
}

.radian-builder-choices {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.5rem;
}

.radian-builder-choices .choice-button {
  min-width: 0;
  min-height: 3rem;
  padding-inline: 0.45rem;
}

.radian-builder-feedback {
  min-height: 2.4rem;
  margin: 0 !important;
  padding: 0 !important;
}

.radian-builder-result {
  display: grid;
  gap: 0.5rem;
  padding: 0.75rem;
  border-radius: 12px;
  background: #0e2d18;
  box-shadow: inset 0 0 0 1px #30d15866;
  color: var(--apple-label, #f5f5f7);
}

.radian-builder-result > span {
  min-width: 0;
  overflow-x: auto;
  scrollbar-width: none;
}

#radian-derivation-visual.is-reconstructed .radian-recovery-chain {
  box-shadow: inset 0 0 0 1px #30d15888, 0 0 1.3rem #30d1581c;
}

@media (max-width: 720px) {
  .radian-derivation-visual {
    inset: 0.5rem;
    grid-template-rows: minmax(5.8rem, 0.85fr) auto auto auto auto;
    gap: 0.38rem;
    padding: 0.65rem;
  }

  .radian-visual-orbit {
    min-height: 5.8rem;
  }

  .radian-visual-orbit svg {
    transform: scaleY(0.83);
    transform-origin: bottom;
  }

  .radian-pipeline {
    grid-template-columns: 1fr;
    gap: 0.35rem;
  }

  .radian-same-angle {
    grid-template-columns: auto auto auto;
    justify-self: center;
  }

  .radian-same-angle svg {
    display: none;
  }

  .radian-transfer-row {
    gap: 0.3rem;
  }

  .radian-recovery-chain {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 0.12rem;
    padding-inline: 0.35rem;
  }

  .radian-recovery-chain > span {
    width: 4.15rem;
    flex: 0 0 4.15rem;
  }

  .radian-recovery-chain small {
    font-size: 0.61rem;
  }

  .radian-builder-heading {
    grid-template-columns: auto minmax(0, 1fr);
  }

  .radian-builder-anchor {
    grid-column: 1 / -1;
    padding-left: 3rem;
  }

  .radian-builder-choices {
    grid-template-columns: 1fr;
  }
}

@media (prefers-reduced-motion: reduce) {
  .radian-derivation-visual *,
  .radian-derivation-visual,
  .radian-recall-builder * {
    transition-duration: 180ms !important;
  }
}

/* One semantic beat at a time. The learner never has to search a finished
   wall of formulas while the narration is talking about one small change. */
.radian-derivation-visual {
  display: block;
  container-type: inline-size;
}

.radian-beat {
  position: absolute;
  inset: clamp(0.8rem, 3vw, 1.6rem);
  display: grid;
  min-width: 0;
  place-content: center;
  justify-items: center;
  gap: clamp(0.65rem, 2vw, 1rem);
  pointer-events: none;
  text-align: center;
  transition: opacity 220ms ease-out, transform 360ms cubic-bezier(0.22, 1, 0.36, 1);
}

.radian-beat > small {
  color: var(--apple-secondary, #aeaeb2);
  font-size: clamp(0.68rem, 2.5vw, 0.82rem);
  font-weight: 650;
  letter-spacing: 0.045em;
  text-transform: uppercase;
}

.radian-goal-beat {
  opacity: var(--melo-radian-goal, 0);
  transform: scale(calc(0.96 + var(--melo-radian-goal, 0) * 0.04));
}

.radian-goal-expression {
  display: flex;
  align-items: center;
  gap: clamp(1rem, 5vw, 2.4rem);
  font-size: clamp(2rem, 10cqw, 4.1rem);
}

.radian-goal-expression > span {
  color: var(--apple-tertiary, #8e8e93);
}

.radian-goal-question {
  color: var(--apple-blue, #2997ff);
}

.radian-one-beat {
  opacity: var(--melo-radian-one, 0);
  transform: translateY(calc((1 - var(--melo-radian-one, 0)) * 0.55rem));
}

.radian-one-expression {
  color: var(--apple-label, #f5f5f7);
  font-size: clamp(1.8rem, 8cqw, 3.55rem);
}

.radian-one-beat p {
  margin: 0;
  color: var(--apple-secondary, #aeaeb2);
  font-size: clamp(0.84rem, 3cqw, 1.05rem);
}

.radian-many-ones {
  color: var(--apple-blue, #2997ff);
  font-size: clamp(1rem, 4cqw, 1.55rem);
  opacity: var(--melo-radian-many-ones, 0);
  transform: translateY(calc((1 - var(--melo-radian-many-ones, 0)) * 0.4rem));
}

.radian-identity-beat {
  grid-template-rows: auto auto;
  align-content: center;
  opacity: var(--melo-radian-identity, 0);
  transform: translateY(calc((1 - var(--melo-radian-identity, 0)) * 0.45rem));
}

.radian-identity-beat .radian-visual-orbit {
  width: min(100%, 22rem);
  height: clamp(8rem, 22cqw, 12rem);
  min-height: 0;
}

.radian-identity-visual {
  grid-template-columns: auto auto auto auto auto;
  opacity: 1;
  transform: none;
}

.radian-identity-degree-fraction {
  color: var(--apple-label, #f5f5f7);
  font-size: clamp(1rem, 4cqw, 1.42rem);
  opacity: var(--melo-radian-equal-fraction, 0);
}

.radian-identity-morph,
.radian-identity-fraction {
  opacity: var(--melo-radian-unit-replacement, 0);
  transform: translateX(calc((1 - var(--melo-radian-unit-replacement, 0)) * -0.45rem));
}

.radian-identity-morph {
  color: var(--apple-tertiary, #8e8e93);
}

.radian-identity-visual small {
  opacity: var(--melo-radian-unit-replacement, 0);
}

.radian-pipeline {
  grid-template-columns: 1fr;
  align-content: center;
  opacity: var(--melo-radian-pipeline, 0);
  transform: translateY(calc((1 - var(--melo-radian-pipeline, 0)) * 0.5rem));
}

.radian-pipeline-expression {
  flex-wrap: wrap;
  row-gap: 0.8rem;
  white-space: normal;
}

.radian-pipeline-equals {
  color: var(--apple-tertiary, #8e8e93);
}

.radian-numeric-simplification {
  color: var(--apple-blue, #2997ff);
  opacity: var(--melo-radian-numeric, 0);
}

.radian-pipeline-result {
  font-size: clamp(1.25rem, 5cqw, 2rem);
}

.radian-pipeline > p {
  margin: 0;
  color: var(--apple-secondary, #aeaeb2);
  font-size: clamp(0.75rem, 2.7cqw, 0.95rem);
  opacity: var(--melo-radian-sixty-result, 0);
}

.radian-application-beat {
  opacity: var(--melo-radian-application, 0);
  transform: translateY(calc((1 - var(--melo-radian-application, 0)) * 0.45rem));
}

.radian-transfer-row {
  display: flex;
  width: max-content;
  max-width: 100%;
  grid-template-columns: none;
  justify-content: center;
  gap: clamp(0.5rem, 2vw, 0.9rem);
  padding: 0;
  border: 0;
  color: var(--apple-label, #f5f5f7);
  font-size: clamp(1rem, 4cqw, 1.5rem);
}

.radian-transfer-row strong {
  color: var(--apple-blue, #2997ff);
  text-align: left;
}

.radian-recovery-beat {
  opacity: var(--melo-radian-recovery, 0);
  transform: translateY(calc((1 - var(--melo-radian-recovery, 0)) * 0.45rem));
}

.radian-recovery-chain {
  width: min(100%, 29rem);
  grid-template-columns: 1fr auto 1fr auto 1fr;
  opacity: 1;
  transform: none;
}

@media (max-width: 720px) {
  .radian-beat {
    inset: 0.65rem;
  }

  .radian-identity-beat {
    grid-template-rows: auto auto;
  }

  .radian-identity-beat .radian-visual-orbit {
    width: min(100%, 18rem);
    height: clamp(6.2rem, 38cqw, 9rem);
    min-height: 0;
  }

  .radian-identity-visual {
    grid-template-columns: auto auto minmax(0, auto);
    gap: 0.38rem;
  }

  .radian-identity-morph {
    grid-column: 1 / -1;
    transform: rotate(90deg);
  }

  .radian-identity-fraction {
    grid-column: 1 / -1;
  }

  .radian-recovery-chain {
    display: grid;
    grid-template-columns: 1fr auto 1fr auto 1fr;
  }

  .radian-recovery-chain > span {
    width: auto;
    min-width: 0;
  }
}

/* Hidden authoring surface: ⌘⇧K / Ctrl⇧K. It stays outside the learner flow. */
.lesson-admin-dialog {
  width: min(27rem, calc(100% - 1.5rem));
  max-height: min(48rem, calc(100dvh - 1.5rem));
  margin: auto;
  padding: 0;
  overflow: hidden;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius-lg);
  background: #111113;
  color: var(--cream);
}

.lesson-admin-dialog[open] {
  display: flex;
  flex-direction: column;
  animation: lesson-admin-enter 180ms var(--ease-out) both;
}

.lesson-admin-dialog::backdrop {
  background: rgb(0 0 0 / 78%);
}

.lesson-admin-head,
.lesson-admin-footer {
  display: flex;
  flex: 0 0 auto;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-md);
  padding: 1rem;
}

.lesson-admin-head {
  border-bottom: 1px solid var(--line);
}

.lesson-admin-head h2,
.lesson-admin-head p,
.lesson-admin-shortcut {
  margin: 0;
}

.lesson-admin-head h2 {
  font-size: 1.125rem;
  line-height: 1.2;
}

.lesson-admin-label {
  display: block;
  margin-bottom: 0.2rem;
  color: var(--cream-dim);
  font-size: 0.75rem;
  font-weight: 650;
}

.lesson-admin-close {
  display: grid;
  width: 2.75rem;
  height: 2.75rem;
  flex: 0 0 2.75rem;
  place-items: center;
  border: 0;
  border-radius: var(--radius-sm);
  background: var(--surface-raised);
  color: var(--cream-muted);
  cursor: pointer;
  font-size: 1.5rem;
  line-height: 1;
}

.lesson-admin-position {
  display: grid;
  flex: 0 0 auto;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.25rem;
  margin: 0.75rem 1rem 0;
  padding: 0.25rem;
  border-radius: var(--radius-md);
  background: var(--surface);
}

.lesson-admin-position button,
.lesson-admin-step-button,
.lesson-admin-clip-button,
#lesson-admin-reset {
  min-height: 2.75rem;
  border: 0;
  border-radius: var(--radius-sm);
  color: var(--cream-muted);
  cursor: pointer;
}

.lesson-admin-position button {
  background: transparent;
  font-size: 0.8125rem;
  font-weight: 750;
}

.lesson-admin-position button[aria-pressed="true"] {
  background: var(--surface-soft);
  color: var(--cream);
}

.lesson-admin-steps {
  min-height: 0;
  margin-top: 0.75rem;
  overflow-y: auto;
  overscroll-behavior: contain;
  scrollbar-gutter: stable;
}

.lesson-admin-step {
  border-top: 1px solid var(--line);
}

.lesson-admin-step:first-child {
  border-top: 0;
}

.lesson-admin-step.is-current {
  background: rgb(41 151 255 / 6%);
}

.lesson-admin-step-button,
.lesson-admin-clip-button {
  width: 100%;
  text-align: left;
}

.lesson-admin-step-button {
  display: flex;
  align-items: baseline;
  gap: 0.75rem;
  padding: 0.75rem 1rem;
  background: transparent;
}

.lesson-admin-step-button strong {
  flex: 0 0 3.8rem;
  color: var(--cream);
  font-size: 0.875rem;
}

.lesson-admin-step-button span {
  overflow: hidden;
  color: var(--cream-muted);
  font-size: 0.8125rem;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.lesson-admin-clip-list {
  display: grid;
  gap: 0.125rem;
  padding: 0 0.5rem 0.65rem;
}

.lesson-admin-clip-button {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-md);
  padding: 0.6rem 0.75rem;
  background: transparent;
  font-size: 0.8125rem;
}

.lesson-admin-clip-button small {
  flex: 0 0 auto;
  color: var(--cream-dim);
  font-variant-numeric: tabular-nums;
}

.lesson-admin-step-button:hover,
.lesson-admin-clip-button:hover,
#lesson-admin-reset:hover {
  background: var(--surface-raised);
  color: var(--cream);
}

.lesson-admin-clip-button.is-current,
.lesson-admin-step-button[aria-current="true"] {
  background: var(--blue-soft);
  color: var(--cream);
}

.lesson-admin-status {
  min-height: 2.75rem;
  margin: 0;
  padding: 0.75rem 1rem;
  border-top: 1px solid var(--line);
  color: var(--cream-muted);
  font-size: 0.8125rem;
  line-height: 1.45;
}

.lesson-admin-footer {
  padding-top: 0.75rem;
  border-top: 1px solid var(--line);
}

.lesson-admin-shortcut {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.3rem;
  color: var(--cream-dim);
  font-size: 0.6875rem;
}

.lesson-admin-shortcut kbd {
  padding: 0.15rem 0.35rem;
  border: 1px solid var(--line-strong);
  border-radius: 0.3rem;
  background: var(--surface);
  color: var(--cream-muted);
  font: 650 0.6875rem ui-monospace, "SFMono-Regular", Consolas, monospace;
}

#lesson-admin-reset {
  flex: 0 0 auto;
  padding: 0.5rem 0.75rem;
  background: transparent;
  font-size: 0.75rem;
  font-weight: 700;
}

@keyframes lesson-admin-enter {
  from {
    opacity: 0;
    transform: translateY(0.5rem) scale(0.985);
  }
  to {
    opacity: 1;
    transform: translateY(0) scale(1);
  }
}

@media (max-width: 430px) {
  .lesson-admin-dialog {
    width: calc(100% - 1rem);
    max-height: calc(100dvh - 1rem);
    border-radius: var(--radius-md);
  }

  .lesson-admin-step-button span {
    white-space: normal;
  }

  .lesson-admin-footer {
    align-items: flex-start;
  }
}

@media (prefers-reduced-motion: reduce) {
  .lesson-admin-dialog[open] {
    animation: none;
  }
}

/* Confidence is evidence, not a score. Keep it compact and visually quieter
   than the lesson's mathematical choices. */
.confidence-check {
  margin-top: 1rem;
  padding-top: 1rem;
  border-top: 1px solid var(--apple-separator, #ffffff18);
}

.confidence-check > p {
  margin: 0 0 0.7rem;
  color: var(--apple-secondary, #a1a1a6);
  font-size: 0.9rem;
  line-height: 1.45;
}

.confidence-check > p strong {
  color: var(--apple-label, #f5f5f7);
  font-weight: 650;
}

.confidence-choices {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.55rem;
}

.confidence-choices .choice-button {
  min-width: 0;
  padding-inline: 0.75rem;
}

.confidence-choices .choice-button.is-recorded,
.confidence-choices .choice-button[aria-pressed="true"] {
  background: #0a2f52;
  box-shadow: inset 0 0 0 1px #2997ff8c;
  color: #8fcdff;
}

.completion-confidence {
  max-width: 42rem;
  margin-inline: auto;
  padding: 1rem;
  border: 1px solid var(--apple-separator, #ffffff18);
  border-radius: 12px;
  background: var(--apple-surface, #1c1c1e);
}

.confidence-feedback {
  min-height: 1.3rem;
  margin-top: 0.7rem !important;
  margin-bottom: 0 !important;
  color: var(--apple-tertiary, #707075) !important;
  font-size: 0.8125rem !important;
}

@media (max-width: 720px) {
  .confidence-choices {
    grid-template-columns: 1fr;
  }

  .confidence-choices .choice-button {
    min-height: 2.75rem;
  }
}

/* Full-circle mobile layout: HTML annotations retain their actual font size.
   They share the existing media phases, never a second entrance animation. */
.transfer-mobile-annotations,
.transfer-mobile-equations {
  display: none;
}

@media (max-width: 720px), (max-width: 1000px) and (max-height: 500px) {
  #step-5 .transfer-stage[data-melo-clip="full-circle-bridge"] {
    min-height: 0;
    grid-template-columns: minmax(0, 1fr);
    grid-template-rows: auto auto;
    align-content: start;
    gap: 0.65rem;
    padding: 0.75rem 0.5rem 0.9rem;
  }

  #step-5 .transfer-stage[data-melo-clip="full-circle-bridge"] > #transfer-circle-map,
  #step-5 .transfer-stage[data-melo-clip="full-circle-bridge"] > .transfer-mobile-annotations {
    grid-area: 1 / 1;
    width: min(100%, 25rem);
    max-width: none;
    aspect-ratio: 1;
    transform: none !important;
  }

  #step-5 .transfer-stage[data-melo-clip="full-circle-bridge"] .transfer-bridge-full :is(.transfer-reference-label, .transfer-reference-equation),
  #step-5 .transfer-stage[data-melo-clip="full-circle-bridge"] .transfer-sign-label {
    display: none;
  }

  #step-5 .transfer-stage[data-melo-clip="full-circle-bridge"] > .transfer-mobile-annotations {
    position: relative;
    z-index: 2;
    display: block;
    pointer-events: none;
    color: #d1d1d6;
    font: 650 12px/1.4 -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  }

  .transfer-mobile-angles,
  .transfer-mobile-signs {
    position: absolute;
    inset: 0;
  }

  .transfer-mobile-angles {
    opacity: var(--melo-transfer-full-reference, 0);
  }

  .transfer-mobile-annotations span {
    position: absolute;
    white-space: nowrap;
  }

  .transfer-mobile-angle-known { right: 3%; top: 25%; opacity: var(--melo-transfer-full-known, 0); }
  .transfer-mobile-angle-left { left: 14%; top: 74%; transform: translateX(-50%); opacity: var(--melo-transfer-full-left, 0); }
  .transfer-mobile-angle-right { right: 14%; top: 74%; transform: translateX(50%); opacity: var(--melo-transfer-full-right, 0); }

  .transfer-mobile-signs { opacity: max(var(--melo-transfer-sign-guide, 0), var(--melo-transfer-negative-cue, 0)); }
  .transfer-mobile-signs span { opacity: var(--melo-transfer-sign-guide, 0); }
  .transfer-mobile-sign-x-negative { left: 0; top: 50%; transform: translateY(-50%); }
  .transfer-mobile-sign-x-positive { right: 0; top: 50%; transform: translateY(-50%); }
  .transfer-mobile-sign-y-positive { left: 50%; top: 4%; transform: translateX(-50%); }
  .transfer-mobile-signs .transfer-mobile-sign-y-negative { left: 50%; bottom: 4%; transform: translateX(-50%); opacity: max(var(--melo-transfer-sign-guide, 0), var(--melo-transfer-negative-cue, 0)); }

  #step-5 .transfer-stage[data-melo-clip="full-circle-bridge"] > .transfer-mobile-equations {
    grid-area: 2 / 1;
    display: grid;
    width: min(100%, 25rem);
    gap: 0.35rem;
    padding-top: 0.65rem;
    color: var(--apple-orange, #ff9f0a);
    font-size: 16px;
    line-height: 1.5;
    font-weight: 600;
    font-variant-numeric: tabular-nums;
    text-align: center;
    opacity: var(--melo-transfer-full-reference, 0);
  }

  .transfer-mobile-equations p { margin: 0; white-space: nowrap; }
  .transfer-mobile-equations [data-full-equation="left"] { opacity: var(--melo-transfer-full-left, 0); }
  .transfer-mobile-equations [data-full-equation="right"] { opacity: var(--melo-transfer-full-right, 0); }
}