:root {
  color-scheme: light;
  --paper: #f4f7fa;
  --plot: #fbfcfe;
  --panel: #ffffff;
  --panel-alt: #eef3f7;
  --ink: #102331;
  --ink-soft: #405462;
  --muted: #71818d;
  --rule: #cfd9e1;
  --grid-minor: #edf1f4;
  --grid-major: #dce4ea;
  --fixed: #5c6b76;
  --construction: #1c6ff2;
  --moving: #e5682d;
  --locus: #168a61;
  --locus-soft: #dff2ea;
  --focus-ring: #ffe6d8;
  --danger: #b83a31;
  --display: Cambria, "Times New Roman", serif;
  --body: "Segoe UI Variable Text", Aptos, "Segoe UI", sans-serif;
  --utility: Bahnschrift, "Arial Narrow", "Segoe UI", sans-serif;
}

* {
  box-sizing: border-box;
}

html,
body {
  min-width: 320px;
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--body);
}

button,
input,
summary {
  font: inherit;
}

button,
input[type="range"],
input[type="checkbox"],
summary {
  accent-color: var(--construction);
}

button:focus-visible,
input:focus-visible,
summary:focus-visible,
a:focus-visible {
  outline: 3px solid rgba(28, 111, 242, 0.28);
  outline-offset: 3px;
}

.instrument-app {
  display: grid;
  grid-template-rows: auto auto minmax(0, 1fr) auto;
  height: 100svh;
  min-height: 100svh;
  overflow: hidden;
  background: var(--paper);
}

.topbar {
  display: flex;
  min-height: 58px;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  padding: 0 30px;
  border-bottom: 1px solid var(--rule);
  background: var(--panel);
}

.identity {
  display: flex;
  min-width: 0;
  align-items: baseline;
  gap: 10px;
  font-family: var(--utility);
  font-size: 13px;
  font-weight: 600;
  letter-spacing: 0.11em;
  text-transform: uppercase;
}

.identity a {
  color: var(--ink);
  text-decoration: none;
}

.identity-separator,
.identity-scene {
  color: var(--muted);
}

.topbar-status {
  display: flex;
  align-items: baseline;
  gap: 7px;
  font-family: var(--utility);
}

.step-number {
  min-width: 28px;
  color: var(--construction);
  font-size: 20px;
  font-weight: 700;
  letter-spacing: 0.04em;
}

.step-total {
  color: var(--muted);
  font-size: 13px;
  letter-spacing: 0.08em;
}

.step-rail {
  position: relative;
  display: grid;
  grid-template-columns: repeat(8, minmax(0, 1fr));
  gap: 0;
  padding: 0 30px;
  border-bottom: 1px solid var(--rule);
  background: var(--panel);
}

.step-rail::before {
  position: absolute;
  right: 30px;
  bottom: 0;
  left: 30px;
  height: 2px;
  background: var(--rule);
  content: "";
}

.step-tab {
  position: relative;
  z-index: 1;
  display: grid;
  min-height: 58px;
  place-content: center start;
  gap: 2px;
  padding: 8px 10px 10px;
  border: 0;
  border-bottom: 3px solid transparent;
  background: transparent;
  color: var(--muted);
  cursor: pointer;
  text-align: left;
}

.step-tab:hover {
  color: var(--ink);
}

.step-tab[aria-current="step"] {
  border-bottom-color: var(--construction);
  color: var(--ink);
}

.step-tab-index {
  font-family: var(--utility);
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.12em;
}

.step-tab-label {
  overflow: hidden;
  font-size: 13px;
  font-weight: 600;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.workspace {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(300px, 27vw);
  min-height: 0;
}

.stage-shell {
  position: relative;
  display: grid;
  min-width: 0;
  min-height: 0;
  place-items: center;
  overflow: hidden;
  padding: 18px 20px 14px 28px;
  border-right: 1px solid var(--rule);
  background: var(--paper);
}

.stage-frame {
  position: relative;
  width: 100%;
  height: 100%;
  min-height: 0;
  overflow: hidden;
  border: 1px solid var(--rule);
  border-radius: 6px;
  background: var(--plot);
  box-shadow: 0 12px 32px rgba(24, 48, 66, 0.07);
}

.stage-frame::after {
  position: absolute;
  inset: 10px;
  border: 1px solid rgba(92, 107, 118, 0.12);
  border-radius: 2px;
  content: "";
  pointer-events: none;
}

.geometry-stage {
  display: block;
  width: 100%;
  height: 100%;
}

.geometry-stage text {
  fill: var(--ink);
  font-family: var(--utility);
  font-size: 18px;
  font-weight: 500;
  paint-order: stroke;
  stroke: var(--plot);
  stroke-linejoin: round;
  stroke-width: 6px;
}

.geometry-stage .axis-label,
.geometry-stage .tick-label {
  fill: var(--muted);
  font-family: var(--body);
  font-size: 15px;
  font-weight: 400;
  stroke-width: 5px;
}

.geometry-stage .minor-grid {
  stroke: var(--grid-minor);
  stroke-width: 1;
}

.geometry-stage .major-grid {
  stroke: var(--grid-major);
  stroke-width: 1.25;
}

.geometry-stage .axis {
  stroke: var(--ink-soft);
  stroke-width: 1.7;
}

.geometry-stage .fixed-line {
  fill: none;
  stroke: var(--fixed);
  stroke-dasharray: 11 9;
  stroke-width: 2.8;
}

.geometry-stage .fixed-point {
  fill: var(--plot);
  stroke: var(--fixed);
  stroke-width: 3.5;
}

.geometry-stage .focus-halo {
  fill: var(--focus-ring);
  opacity: 0.85;
}

.geometry-stage .construction-line {
  fill: none;
  stroke: var(--construction);
  stroke-width: 2.6;
}

.geometry-stage .construction-guide {
  fill: none;
  stroke: var(--construction);
  stroke-dasharray: 7 7;
  stroke-width: 2;
  opacity: 0.78;
}

.geometry-stage .right-angle {
  fill: none;
  stroke: var(--construction);
  stroke-width: 2.2;
}

.geometry-stage .moving-point {
  fill: var(--plot);
  stroke: var(--moving);
  stroke-width: 4;
}

.geometry-stage .moving-core {
  fill: var(--moving);
}

.geometry-stage .locus-line {
  fill: none;
  stroke: var(--locus);
  stroke-linecap: round;
  stroke-linejoin: round;
  stroke-width: 5;
}

.geometry-stage .history-dot {
  fill: var(--locus);
  opacity: 0.24;
}

.geometry-stage .distance-line,
.geometry-stage .distance-tick {
  fill: none;
  stroke: var(--locus);
  stroke-width: 2.8;
}

.geometry-stage .projection-line {
  fill: none;
  stroke: var(--construction);
  stroke-dasharray: 5 6;
  stroke-width: 2;
  opacity: 0.76;
}

.geometry-stage .sample-point {
  fill: var(--plot);
  stroke: var(--moving);
  stroke-width: 3;
}

.geometry-stage .sample-point.is-origin {
  fill: var(--moving);
}

.geometry-stage .sample-label {
  fill: var(--moving);
  font-size: 15px;
  stroke-width: 5px;
}

.geometry-stage .locus-preview {
  fill: none;
  stroke: var(--locus);
  stroke-dasharray: 6 7;
  stroke-linecap: round;
  stroke-width: 3;
  opacity: 0.3;
}

.geometry-stage .telemetry-rule {
  stroke: var(--rule);
  stroke-width: 1.2;
}

.geometry-stage .telemetry-label,
.geometry-stage .telemetry-value {
  font-family: var(--utility);
  font-size: 15px;
  letter-spacing: 0.06em;
  stroke-width: 5px;
}

.geometry-stage .telemetry-label {
  fill: var(--muted);
}

.geometry-stage .telemetry-value {
  fill: var(--construction);
  font-weight: 700;
}

.geometry-stage .secondary-locus {
  fill: none;
  stroke: var(--construction);
  stroke-linecap: round;
  stroke-linejoin: round;
  stroke-width: 4;
}

.geometry-stage .reflected-locus {
  fill: none;
  stroke: var(--construction);
  stroke-dasharray: 10 7;
  stroke-linecap: round;
  stroke-linejoin: round;
  stroke-width: 3.2;
  opacity: 0.62;
}

.geometry-stage .secant-line {
  fill: none;
  stroke: var(--moving);
  stroke-width: 3.2;
}

.geometry-stage .tangent-line {
  fill: none;
  stroke: var(--locus);
  stroke-width: 4;
}

.geometry-stage .asymptote-line,
.geometry-stage .directrix-line {
  fill: none;
  stroke: var(--fixed);
  stroke-dasharray: 10 8;
  stroke-width: 2.2;
}

.geometry-stage .directrix-line.is-paired {
  stroke: var(--construction);
  stroke-dasharray: 6 6;
  stroke-width: 2;
  opacity: 0.78;
}

.geometry-stage .directrix-label,
.geometry-stage .directrix-note {
  fill: var(--construction);
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.06em;
  stroke-width: 5px;
}

.geometry-stage .directrix-note {
  fill: var(--muted);
  font-size: 11px;
}

.geometry-stage .directrix-distance {
  fill: none;
  stroke: var(--construction);
  stroke-dasharray: 5 5;
  stroke-width: 2.2;
}

.geometry-stage .directrix-distance.is-second {
  stroke: var(--moving);
}

.geometry-stage .directrix-foot {
  fill: var(--plot);
  stroke: var(--construction);
  stroke-width: 2.4;
}

.geometry-stage .directrix-foot-label,
.geometry-stage .directrix-measure {
  fill: var(--construction);
  font-size: 13px;
  font-weight: 700;
  stroke-width: 5px;
}

.geometry-stage .directrix-measure {
  fill: var(--ink-soft);
  font-size: 12px;
}

.geometry-stage .feature-marker {
  fill: var(--plot);
  stroke: var(--construction);
  stroke-width: 3;
}

.geometry-stage .feature-marker.is-focus {
  fill: var(--moving);
  stroke: var(--plot);
}

.geometry-stage .panel-divider,
.geometry-stage .formula-rule {
  stroke: var(--rule);
  stroke-width: 1.4;
}

.geometry-stage .panel-title,
.geometry-stage .formula-label,
.geometry-stage .clue-label {
  fill: var(--muted);
  font-family: var(--utility);
  font-size: 14px;
  font-weight: 700;
  letter-spacing: 0.12em;
  stroke-width: 5px;
}

.geometry-stage .live-measure {
  fill: var(--moving);
  font-family: var(--utility);
  font-size: 16px;
  font-weight: 700;
  stroke-width: 5px;
}

.geometry-stage .result-measure {
  fill: var(--locus);
  font-family: var(--utility);
  font-size: 17px;
  font-weight: 700;
  stroke-width: 5px;
}

.geometry-stage .clue-plate {
  fill: var(--panel);
  stroke: var(--rule);
  stroke-width: 1.5;
}

.geometry-stage .clue-plate.is-live {
  fill: #f1f6ff;
  stroke: var(--construction);
  stroke-width: 2;
}

.geometry-stage .clue-value {
  fill: var(--ink);
  font-family: var(--display);
  font-size: 23px;
  font-weight: 400;
  stroke-width: 6px;
}

.geometry-stage .answer-seal {
  fill: var(--locus-soft);
  stroke: var(--locus);
  stroke-width: 2.5;
}

.geometry-stage .answer-label {
  fill: var(--locus);
  font-family: var(--utility);
  font-size: 21px;
  font-weight: 700;
  letter-spacing: 0.08em;
  stroke-width: 5px;
}

.geometry-stage .svg-math {
  display: grid;
  width: 100%;
  height: 100%;
  place-items: center;
  padding: 8px 14px;
  color: var(--ink);
  font-family: var(--body);
  font-size: 16px;
  text-align: center;
}

.geometry-stage .svg-math .katex {
  font-size: 1.18em;
}

.geometry-stage .svg-math.is-sealed {
  color: var(--muted);
  font-family: var(--utility);
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.geometry-stage .classification-zone {
  stroke: var(--rule);
  stroke-width: 1;
}

.geometry-stage .classification-zone.is-ellipse {
  fill: var(--locus-soft);
}

.geometry-stage .classification-zone.is-neutral {
  fill: var(--panel-alt);
}

.geometry-stage .classification-zone.is-boundary {
  fill: var(--focus-ring);
}

.geometry-stage .classification-zone.is-hyperbola {
  fill: #e9f1ff;
}

.geometry-stage .classification-marker {
  fill: var(--moving);
  stroke: var(--plot);
  stroke-width: 2;
}

.geometry-stage .ratio-ray {
  fill: none;
  stroke: var(--moving);
  stroke-width: 2.8;
}

.geometry-stage .cone-wire,
.geometry-stage .cone-rim {
  fill: none;
  stroke: var(--fixed);
  stroke-width: 1.6;
  opacity: 0.42;
}

.geometry-stage .cone-facet {
  fill: url(#cone-light);
  stroke: none;
  pointer-events: none;
}

.geometry-stage .cone-facet.is-front {
  opacity: 0.13;
}

.geometry-stage .cone-facet.is-back {
  opacity: 0.035;
}

.geometry-stage .cone-wire.is-front {
  opacity: 0.54;
}

.geometry-stage .cone-wire.is-back {
  opacity: 0.18;
}

.geometry-stage .cone-rim {
  stroke-width: 2.2;
  opacity: 0.7;
}

.geometry-stage .cone-generator {
  fill: none;
  stroke: var(--moving);
  stroke-dasharray: 7 6;
  stroke-width: 2.5;
}

.geometry-stage .plane-surface {
  fill: url(#plane-light);
  fill-opacity: 0.2;
  stroke: var(--construction);
  stroke-width: 2.2;
}

.geometry-stage .intersection-curve {
  fill: none;
  stroke: var(--moving);
  stroke-linecap: round;
  stroke-linejoin: round;
  stroke-width: 5;
  filter: url(#curve-glow);
}

.geometry-stage .section-frame {
  fill: var(--panel);
  fill-opacity: 0.42;
  stroke: var(--rule);
  stroke-width: 1.5;
}

.geometry-stage .section-curve {
  fill: none;
  stroke: var(--locus);
  stroke-linecap: round;
  stroke-linejoin: round;
  stroke-width: 4.5;
}

/* Scene 07: eccentricity and focal-distance invariants */
.geometry-stage .feature-marker.is-centre {
  fill: var(--ink);
  stroke: var(--plot);
  stroke-width: 2;
}

.geometry-stage .feature-marker.is-vertex {
  fill: var(--plot);
  stroke: var(--fixed);
  stroke-width: 2.5;
}

.geometry-stage .feature-label,
.geometry-stage .moving-label {
  fill: var(--ink-soft);
  font-size: 15px;
  font-weight: 700;
  stroke-width: 5px;
}

.geometry-stage .feature-label.is-focus,
.geometry-stage .moving-label {
  fill: var(--moving);
}

.geometry-stage .dimension-base,
.geometry-stage .dimension-focus {
  stroke-linecap: round;
}

.geometry-stage .dimension-base {
  stroke: var(--construction);
  stroke-width: 5;
}

.geometry-stage .dimension-focus {
  stroke: var(--moving);
  stroke-width: 4;
}

.geometry-stage .dimension-centre,
.geometry-stage .dimension-vertex {
  fill: var(--plot);
  stroke: var(--construction);
  stroke-width: 2.5;
}

.geometry-stage .dimension-focus-dot {
  fill: var(--moving);
  stroke: var(--plot);
  stroke-width: 2;
}

.geometry-stage .dimension-label {
  fill: var(--muted);
  font-size: 13px;
  font-weight: 700;
  stroke-width: 4px;
}

.geometry-stage .dimension-label.is-focus {
  fill: var(--moving);
}

.geometry-stage .distance-line.is-first {
  stroke: var(--construction);
}

.geometry-stage .distance-line.is-second {
  stroke: var(--moving);
  stroke-dasharray: 8 5;
}

.geometry-stage .distance-readout {
  fill: var(--ink-soft);
  font-size: 15px;
  font-weight: 700;
  stroke-width: 5px;
}

.geometry-stage .proof-seal {
  fill: var(--panel);
  stroke: var(--locus);
  stroke-width: 1.7;
}

.geometry-stage .proof-seal-label {
  fill: var(--muted);
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.12em;
  stroke-width: 4px;
}

.geometry-stage .proof-seal-value {
  fill: var(--locus);
  font-size: 15px;
  font-weight: 700;
  stroke-width: 4px;
}

.geometry-stage .eccentricity-name {
  fill: var(--construction);
  font-size: 14px;
  font-weight: 700;
  letter-spacing: 0.08em;
  stroke-width: 5px;
}

/* Scene 08: rotatable cone and Dandelin spheres */
.cone-slice-app .geometry-stage {
  cursor: grab;
  touch-action: none;
  user-select: none;
}

.cone-slice-app .geometry-stage.is-dragging {
  cursor: grabbing;
}

.geometry-stage .spatial-backdrop {
  fill: url(#stage-light);
  fill-opacity: 0.72;
  stroke: var(--rule);
  stroke-width: 1.2;
}

.geometry-stage .cone-apex {
  fill: var(--ink);
  stroke: var(--plot);
  stroke-width: 2;
}

.geometry-stage .plane-grid {
  fill: none;
  stroke: var(--construction);
  stroke-width: 1;
  opacity: 0.28;
}

.geometry-stage .dandelin-sphere {
  fill: url(#sphere-light-a);
  fill-opacity: 0.46;
  stroke: var(--construction);
  stroke-width: 2.6;
  filter: url(#sphere-shadow);
}

.geometry-stage .dandelin-sphere.is-secondary {
  fill: url(#sphere-light-b);
  fill-opacity: 0.34;
  stroke: var(--moving);
}

.geometry-stage .sphere-centre {
  fill: var(--ink);
  stroke: var(--plot);
  stroke-width: 2;
}

.geometry-stage .sphere-label,
.geometry-stage .focus-label,
.geometry-stage .tangent-label {
  fill: var(--ink-soft);
  font-size: 14px;
  font-weight: 700;
  stroke-width: 5px;
}

.geometry-stage .sphere-radius {
  stroke: var(--fixed);
  stroke-dasharray: 4 4;
  stroke-width: 1.8;
}

.geometry-stage .focus-contact {
  fill: var(--moving);
  stroke: var(--plot);
  stroke-width: 2.5;
}

.geometry-stage .focus-label {
  fill: var(--moving);
}

.geometry-stage .focus-contact.is-pair-one,
.geometry-stage .tangent-contact.is-pair-one {
  fill: var(--locus);
  stroke: var(--plot);
}

.geometry-stage .focus-contact.is-pair-two,
.geometry-stage .tangent-contact.is-pair-two {
  fill: var(--moving);
  stroke: var(--plot);
}

.geometry-stage .focus-label.is-pair-one,
.geometry-stage .tangent-label.is-pair-one {
  fill: var(--locus);
}

.geometry-stage .focus-label.is-pair-two,
.geometry-stage .tangent-label.is-pair-two {
  fill: var(--moving);
}

.geometry-stage .focal-proof-line {
  stroke-width: 4;
  stroke-linecap: round;
}

.geometry-stage .tangent-proof-line {
  stroke-dasharray: 7 5;
  stroke-width: 3.4;
  stroke-linecap: round;
}

.geometry-stage .focal-proof-line.is-pair-one,
.geometry-stage .tangent-proof-line.is-pair-one,
.geometry-stage .proof-equality-tick.is-pair-one {
  stroke: var(--locus);
}

.geometry-stage .focal-proof-line.is-pair-two,
.geometry-stage .tangent-proof-line.is-pair-two,
.geometry-stage .proof-equality-tick.is-pair-two {
  stroke: var(--moving);
}

.geometry-stage .proof-equality-tick {
  stroke-width: 3.4;
  stroke-linecap: round;
}

.geometry-stage .proof-fixed-line {
  stroke: var(--fixed);
  stroke-linecap: round;
  stroke-width: 8px;
  opacity: 0.28;
}

.geometry-stage .proof-segment-label {
  fill: var(--ink);
  font-size: 14px;
  font-weight: 700;
  paint-order: stroke fill;
  stroke: var(--plot);
  stroke-width: 6px;
  stroke-linejoin: round;
}

.geometry-stage .proof-segment-label.is-fixed {
  fill: var(--fixed);
}

.geometry-stage .proof-visual-note {
  fill: var(--muted);
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.1em;
  paint-order: stroke fill;
  stroke: var(--plot);
  stroke-width: 5px;
}

.geometry-stage .proof-visual-note.is-secondary {
  fill: var(--locus);
}

.geometry-stage .tangent-contact {
  fill: var(--plot);
  stroke: var(--locus);
  stroke-width: 2.5;
}

.geometry-stage.is-proof-view .cone-facet.is-front {
  opacity: 0.045;
}

.geometry-stage.is-proof-view .cone-facet.is-back {
  opacity: 0.008;
}

.geometry-stage.is-proof-view .cone-wire.is-front {
  opacity: 0.14;
}

.geometry-stage.is-proof-view .cone-wire.is-back {
  opacity: 0.035;
}

.geometry-stage.is-proof-view .cone-rim {
  opacity: 0.22;
}

.geometry-stage.is-proof-view .plane-surface {
  fill-opacity: 0.07;
  stroke-width: 1.2;
}

.geometry-stage.is-proof-view .plane-grid {
  opacity: 0.045;
}

.geometry-stage.is-proof-view .cone-generator {
  opacity: 0.45;
}

.geometry-stage .receding-plate {
  fill: var(--panel);
  stroke: var(--moving);
  stroke-width: 1.5;
}

.geometry-stage .receding-label {
  fill: var(--muted);
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.1em;
  stroke-width: 4px;
}

.geometry-stage .receding-value {
  fill: var(--moving);
  font-size: 15px;
  font-weight: 700;
  stroke-width: 4px;
}

.geometry-stage .view-hint {
  fill: var(--muted);
  font-size: 12px;
  font-weight: 600;
  letter-spacing: 0.08em;
  stroke-width: 4px;
}

.ledger {
  display: flex;
  min-width: 0;
  min-height: 0;
  flex-direction: column;
  overflow: auto;
  padding: 28px 28px 22px;
  background: var(--panel);
}

.ledger-section-label {
  margin: 0 0 14px;
  color: var(--construction);
  font-family: var(--utility);
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.14em;
  text-transform: uppercase;
}

.ledger h1 {
  margin: 0;
  font-family: var(--display);
  font-size: clamp(30px, 3.1vw, 48px);
  font-weight: 400;
  line-height: 1.02;
  letter-spacing: -0.025em;
}

.step-kicker {
  margin: 20px 0 7px;
  color: var(--ink);
  font-size: 17px;
  font-weight: 650;
  line-height: 1.35;
}

.step-description {
  margin: 0;
  color: var(--ink-soft);
  font-size: 15px;
  line-height: 1.55;
}

.math-ledger {
  display: grid;
  gap: 10px;
  margin-top: 24px;
  padding: 18px 0 18px 16px;
  border-top: 1px solid var(--rule);
  border-bottom: 1px solid var(--rule);
  border-left: 3px solid var(--construction);
}

.math-ledger[hidden],
.prediction-panel[hidden],
.feedback-line[hidden] {
  display: none;
}

.math-line {
  min-height: 29px;
  color: var(--ink);
  font-size: 17px;
}

.math-line.is-result {
  color: var(--locus);
  font-size: 20px;
}

.math-line .katex {
  font-size: 1.08em;
}

.cone-slice-app.is-proof-step .math-ledger {
  gap: 14px;
  margin-top: 20px;
  padding-block: 22px;
  border-left-width: 4px;
}

.cone-slice-app.is-proof-step .math-line {
  min-height: 34px;
  font-size: 19px;
}

.cone-slice-app.is-proof-step .math-line.is-result {
  font-size: 19px;
}

.cone-slice-app.is-proof-step .math-line .katex {
  font-size: 1.08em;
}

.eccentricity-app .math-line .katex {
  font-size: 0.9em;
}

.prediction-panel {
  display: grid;
  gap: 12px;
  margin-top: 24px;
  padding-top: 20px;
  border-top: 1px solid var(--rule);
}

.prediction-question {
  margin: 0;
  color: var(--ink);
  font-size: 16px;
  font-weight: 650;
  line-height: 1.45;
}

.choice-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 8px;
}

.choice-button {
  min-height: 48px;
  padding: 10px 12px;
  border: 1px solid var(--rule);
  border-radius: 3px;
  background: var(--panel);
  color: var(--ink);
  cursor: pointer;
  font-size: 14px;
  font-weight: 600;
  text-align: left;
}

.choice-button:hover {
  border-color: var(--construction);
  background: #f1f6ff;
}

.choice-button[aria-pressed="true"] {
  border-color: var(--construction);
  background: #e9f1ff;
  box-shadow: inset 3px 0 0 var(--construction);
}

.feedback-line {
  margin: 16px 0 0;
  padding: 11px 12px;
  border-left: 3px solid var(--locus);
  background: var(--locus-soft);
  color: var(--ink);
  font-size: 14px;
  line-height: 1.45;
}

.teacher-cue {
  margin-top: auto;
  padding-top: 18px;
  border-top: 1px solid var(--rule);
}

.teacher-cue summary {
  color: var(--ink);
  cursor: pointer;
  font-family: var(--utility);
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.05em;
  text-transform: uppercase;
}

.cue-list {
  display: grid;
  gap: 10px;
  margin: 15px 0 0;
}

.cue-list div {
  display: grid;
  gap: 2px;
}

.cue-list dt {
  color: var(--muted);
  font-family: var(--utility);
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.cue-list dd {
  margin: 0;
  color: var(--ink-soft);
  font-size: 13px;
  line-height: 1.45;
}

.instrument-rail {
  display: grid;
  grid-template-columns: minmax(260px, 1fr) auto auto;
  gap: 26px;
  align-items: center;
  padding: 14px 28px 16px;
  border-top: 1px solid var(--rule);
  background: var(--panel-alt);
}

.parameter-control {
  display: grid;
  grid-template-columns: auto minmax(150px, 1fr);
  gap: 5px 18px;
  align-items: center;
}

.parameter-label {
  display: flex;
  align-items: baseline;
  gap: 8px;
  color: var(--ink);
  font-family: var(--utility);
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.parameter-value {
  color: var(--construction);
  font-size: 18px;
  letter-spacing: 0;
  text-transform: none;
}

.parameter-control input[type="range"] {
  width: 100%;
  min-width: 140px;
  margin: 0;
}

.parameter-stack {
  display: grid;
  min-width: 300px;
  gap: 7px;
}

.parameter-stack .parameter-control {
  grid-template-columns: 118px minmax(150px, 1fr);
}

.parameter-stack .range-extents {
  display: none;
}

.instrument-rail.is-compact {
  grid-template-columns: minmax(300px, 1fr) auto;
}

.instrument-rail.is-compact .transport {
  justify-self: end;
}

.range-extents {
  grid-column: 2;
  display: flex;
  justify-content: space-between;
  color: var(--muted);
  font-family: var(--utility);
  font-size: 10px;
  letter-spacing: 0.06em;
}

.layer-controls {
  display: flex;
  flex-wrap: wrap;
  gap: 8px 14px;
  align-items: center;
  padding: 0;
  border: 0;
  margin: 0;
}

.mode-controls {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  align-items: end;
}

/* Scene 08: a compact drafting-style layer palette for teacher-controlled reveals. */
.layer-menu {
  position: relative;
  align-self: end;
  font-family: var(--utility);
}

.layer-menu summary {
  display: flex;
  min-width: 138px;
  min-height: 42px;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 0 11px;
  border: 1px solid var(--rule);
  border-radius: 3px;
  background: var(--panel);
  color: var(--ink);
  cursor: pointer;
  font-family: var(--utility);
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.06em;
  list-style: none;
  text-transform: uppercase;
}

.layer-menu summary::-webkit-details-marker {
  display: none;
}

.layer-menu summary::after {
  color: var(--construction);
  content: "▾";
  font-size: 12px;
}

.layer-menu[open] summary {
  border-color: var(--construction);
  box-shadow: inset 0 -3px 0 var(--construction);
}

.layer-menu[open] summary::after {
  content: "▴";
}

.layer-count {
  color: var(--construction);
  font-size: 10px;
  letter-spacing: 0.04em;
  white-space: nowrap;
}

.layer-popover {
  position: absolute;
  z-index: 12;
  right: 0;
  bottom: calc(100% + 10px);
  width: 316px;
  padding: 15px 16px 16px;
  border: 1px solid var(--rule);
  border-radius: 4px;
  background: var(--panel);
  box-shadow: 0 14px 34px rgba(24, 48, 66, 0.16);
}

.layer-popover-title {
  margin: 0 0 12px;
  color: var(--muted);
  font-size: 10px;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.cone-layer-controls {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 11px 14px;
}

.cone-slice-app .layer-popover {
  width: 360px;
  max-width: calc(100vw - 36px);
}

.cone-layer-controls > .layer-group-label {
  grid-column: 1 / -1;
  color: var(--muted);
  font-family: var(--utility);
  font-size: 10px;
  font-weight: 700;
  letter-spacing: 0.11em;
  text-transform: uppercase;
}

.cone-layer-controls > .layer-group-label.is-proof-group {
  margin-top: 3px;
  padding-top: 10px;
  border-top: 1px solid var(--rule);
}

.cone-layer-controls .layer-toggle {
  min-width: 0;
  font-size: 12px;
}

.cone-layer-controls .layer-toggle.is-unavailable {
  cursor: not-allowed;
  opacity: 0.38;
}

.layer-swatch {
  display: inline-grid;
  width: 19px;
  height: 16px;
  flex: 0 0 19px;
  place-items: center;
  color: var(--muted);
  font-size: 9px;
  font-weight: 700;
}

.layer-swatch.is-cone {
  border-right: 1px solid var(--fixed);
  border-left: 1px solid var(--fixed);
  clip-path: polygon(0 0, 100% 50%, 0 100%, 35% 50%);
  background: rgba(92, 107, 118, 0.16);
}

.layer-swatch.is-plane {
  border: 1px solid var(--construction);
  background: rgba(28, 111, 242, 0.12);
  transform: skew(-14deg);
}

.layer-swatch.is-section {
  height: 8px;
  border-bottom: 3px solid var(--moving);
  border-radius: 50%;
}

.layer-swatch.is-sphere {
  width: 16px;
  flex-basis: 19px;
  border: 2px solid var(--construction);
  border-radius: 50%;
  background: rgba(28, 111, 242, 0.1);
}

.layer-swatch.is-focus {
  width: 9px;
  height: 9px;
  margin-inline: 4px 6px;
  flex-basis: 9px;
  border-radius: 50%;
  background: var(--locus);
  box-shadow: 0 0 0 3px var(--locus-soft);
}

.layer-swatch.is-proof {
  color: var(--moving);
  font-size: 14px;
}

.layer-swatch.is-proof-segment {
  position: relative;
}

.layer-swatch.is-proof-segment::before {
  width: 19px;
  border-top: 3px solid var(--locus);
  content: "";
}

.layer-swatch.is-proof-segment.is-pair-two::before {
  border-top-color: var(--moving);
}

.layer-swatch.is-proof-segment.is-tangent::before {
  border-top-style: dashed;
}

.layer-swatch.is-proof-segment.is-fixed::before {
  border-top: 6px solid rgba(92, 107, 118, 0.28);
}

.layer-swatch.is-label {
  color: var(--ink-soft);
  font-family: var(--display);
  font-size: 11px;
}

.select-control {
  display: grid;
  gap: 4px;
  color: var(--muted);
  font-family: var(--utility);
  font-size: 10px;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.select-control select {
  min-width: 132px;
  min-height: 42px;
  padding: 0 34px 0 11px;
  border: 1px solid var(--rule);
  border-radius: 3px;
  background: var(--panel);
  color: var(--ink);
  font-family: var(--body);
  font-size: 13px;
  font-weight: 600;
  letter-spacing: 0;
  text-transform: none;
}

.select-control select:disabled {
  cursor: not-allowed;
  opacity: 0.45;
}

.layer-controls legend {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
}

.layer-toggle {
  display: flex;
  align-items: center;
  gap: 7px;
  color: var(--ink-soft);
  cursor: pointer;
  font-size: 13px;
  font-weight: 600;
  white-space: nowrap;
}

.layer-toggle input {
  width: 17px;
  height: 17px;
  margin: 0;
}

.transport {
  display: flex;
  gap: 7px;
  justify-content: flex-end;
}

.control-button {
  display: inline-flex;
  min-height: 42px;
  align-items: center;
  justify-content: center;
  gap: 7px;
  padding: 0 14px;
  border: 1px solid var(--rule);
  border-radius: 3px;
  background: var(--panel);
  color: var(--ink);
  cursor: pointer;
  font-family: var(--utility);
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.04em;
}

.control-button:hover:not(:disabled) {
  border-color: var(--ink-soft);
}

.control-button.is-primary {
  border-color: var(--ink);
  background: var(--ink);
  color: #ffffff;
}

.control-button.is-play {
  border-color: var(--construction);
  color: var(--construction);
}

.control-button:disabled {
  cursor: not-allowed;
  opacity: 0.38;
}

.button-icon {
  font-size: 16px;
  line-height: 1;
}

.shortcut-note {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  border: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
}

@media (max-width: 1050px) {
  .workspace {
    grid-template-columns: minmax(0, 1fr) 310px;
  }

  .step-tab-label {
    display: none;
  }

  .instrument-rail {
    grid-template-columns: minmax(240px, 1fr) auto;
  }

  .transport {
    grid-column: 1 / -1;
  }
}

@media (max-width: 760px) {
  .instrument-app {
    display: block;
    height: auto;
    min-height: 100svh;
    overflow: visible;
  }

  .topbar {
    padding: 0 16px;
  }

  .identity-scene,
  .identity-separator {
    display: none;
  }

  .step-rail {
    padding: 0 12px;
  }

  .step-rail::before {
    right: 12px;
    left: 12px;
  }

  .step-tab {
    min-height: 48px;
    place-content: center;
    padding-inline: 4px;
    text-align: center;
  }

  .workspace {
    display: block;
  }

  .stage-shell {
    padding: 12px;
    border-right: 0;
    overflow: visible;
  }

  .geometry-stage {
    height: auto;
    aspect-ratio: 25 / 16;
  }

  .stage-frame {
    height: auto;
  }

  .ledger {
    min-height: 360px;
    padding: 24px 18px;
    border-top: 1px solid var(--rule);
    overflow: visible;
  }

  .ledger h1 {
    font-size: 34px;
  }

  .instrument-rail {
    grid-template-columns: 1fr;
    gap: 18px;
    padding: 18px;
  }

  .mode-controls,
  .layer-menu,
  .layer-menu summary {
    width: 100%;
  }

  .layer-popover {
    position: static;
    width: 100%;
    margin-top: 8px;
    box-shadow: none;
  }

  .parameter-control {
    grid-template-columns: 1fr;
  }

  .parameter-stack {
    min-width: 0;
  }

  .parameter-stack .parameter-control {
    grid-template-columns: 1fr;
  }

  .instrument-rail.is-compact {
    grid-template-columns: 1fr;
  }

  .instrument-rail.is-compact .transport {
    justify-self: stretch;
  }

  .range-extents {
    grid-column: 1;
  }

  .transport {
    grid-column: 1;
    justify-content: stretch;
  }

  .control-button {
    flex: 1;
  }
}

@media (max-width: 470px) {
  .cone-layer-controls {
    grid-template-columns: 1fr;
  }

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

  .control-button .button-label {
    display: none;
  }

  .control-button {
    min-width: 44px;
    padding-inline: 12px;
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    scroll-behavior: auto !important;
    transition-duration: 0.01ms !important;
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
  }
}