:root {
  --bg: #101516;
  --ink: #f5f7f2;
  --muted: #a9b2ae;
  --line: rgba(255, 255, 255, 0.14);
  --panel: rgba(10, 14, 15, 0.8);
  --mirror: #2dd4bf;
  --incoming: #fff1b8;
  --reflected: #ffb52e;
  --focus: #ff6b4a;
  --normal: #b8a7ff;
}

* {
  box-sizing: border-box;
}

html,
body {
  width: 100%;
  height: 100%;
  margin: 0;
  overflow: hidden;
  background: var(--bg);
  color: var(--ink);
  font-family: Inter, "Noto Sans SC", "PingFang SC", "Microsoft YaHei", Arial, sans-serif;
}

button,
input {
  font: inherit;
}

#stage,
.v3d-container,
#lesson-canvas-host {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
}

.v3d-container {
  overflow: hidden;
  background: var(--bg);
}

#lesson-canvas-host {
  z-index: 2;
}

#lesson-canvas-host canvas {
  display: block;
  width: 100%;
  height: 100%;
  touch-action: none;
  cursor: grab;
}

#lesson-canvas-host canvas.is-dragging {
  cursor: grabbing;
}

#lesson-ui {
  position: absolute;
  inset: 0;
  z-index: 4;
  pointer-events: none;
  opacity: 1;
  transition: opacity 220ms ease;
}

.ui-hidden #lesson-ui,
.ui-hidden #lesson-canvas-host {
  opacity: 0;
  pointer-events: none;
}

#scene-label-layer {
  position: absolute;
  inset: 0;
  overflow: hidden;
  pointer-events: none;
}

.scene-label {
  --x: 0px;
  --y: 0px;
  --dx: 8px;
  --dy: -16px;
  position: absolute;
  left: 0;
  top: 0;
  transform: translate3d(calc(var(--x) + var(--dx)), calc(var(--y) + var(--dy)), 0);
  color: var(--ink);
  font-family: "Cambria Math", Georgia, "Noto Sans SC", sans-serif;
  font-size: var(--scene-label-size, 13px);
  line-height: 1;
  font-weight: 850;
  white-space: nowrap;
  text-shadow:
    -1px -1px 0 var(--bg),
    1px -1px 0 var(--bg),
    -1px 1px 0 var(--bg),
    1px 1px 0 var(--bg),
    0 2px 8px rgba(0, 0, 0, 0.9);
  opacity: 0;
  will-change: transform;
}

.scene-label.is-visible {
  opacity: 1;
}

.focus-label {
  color: var(--focus);
  font-size: calc(var(--scene-label-size, 13px) * 1.12);
}

.vertex-label {
  color: var(--mirror);
}

.law-label {
  color: var(--normal);
}

.lesson-header {
  position: absolute;
  top: max(14px, env(safe-area-inset-top));
  left: 50%;
  width: min(1120px, calc(100% - 96px));
  transform: translateX(-50%);
  display: grid;
  grid-template-columns: minmax(250px, 1fr) minmax(500px, 620px);
  align-items: center;
  gap: 18px;
  padding: 10px 12px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: rgba(8, 12, 13, 0.66);
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.2);
  backdrop-filter: blur(12px);
  pointer-events: auto;
}

.title-block {
  min-width: 0;
}

.eyebrow {
  margin: 0 0 4px;
  color: var(--reflected);
  font-size: 9px;
  font-weight: 850;
  letter-spacing: 0;
}

h1 {
  margin: 0;
  font-size: clamp(25px, 2.3vw, 38px);
  line-height: 1.08;
  font-weight: 900;
  letter-spacing: 0;
}

.subtitle {
  margin: 5px 0 0;
  color: var(--muted);
  font-size: clamp(11px, 1vw, 15px);
  font-weight: 650;
  letter-spacing: 0;
}

.value-board {
  display: grid;
  grid-template-columns: 1.35fr repeat(3, minmax(82px, 1fr));
  border-top: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
}

.value-item {
  min-width: 0;
  padding: 9px 12px;
  border-left: 1px solid var(--line);
}

.value-item:first-child {
  border-left: 0;
}

.value-item span {
  display: block;
  margin-bottom: 3px;
  color: var(--muted);
  font-size: 9px;
  font-weight: 750;
}

.value-item strong {
  display: block;
  overflow: hidden;
  font-family: "Cambria Math", Georgia, serif;
  font-size: 18px;
  line-height: 1.15;
  font-weight: 900;
  font-variant-numeric: tabular-nums;
  white-space: nowrap;
}

.equation-value strong { color: var(--mirror); }
.focus-value strong { color: var(--focus); }
.angle-value strong { color: var(--incoming); }
.ray-value strong { color: var(--reflected); }

.story-caption {
  position: absolute;
  top: 126px;
  left: 50%;
  min-width: min(520px, calc(100% - 40px));
  transform: translateX(-50%);
  display: grid;
  grid-template-columns: 34px auto;
  grid-template-rows: auto auto;
  column-gap: 10px;
  padding: 8px 14px;
  border-top: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  background: rgba(8, 12, 13, 0.36);
  backdrop-filter: blur(8px);
  text-align: left;
}

.caption-step {
  grid-row: 1 / 3;
  align-self: center;
  color: var(--reflected);
  font-family: Georgia, serif;
  font-size: 24px;
  font-weight: 900;
}

.story-caption strong {
  font-size: 15px;
  font-weight: 900;
}

.story-caption > span:last-child {
  margin-top: 2px;
  color: var(--muted);
  font-size: 11px;
  font-weight: 650;
}

.application-strip {
  position: absolute;
  top: 184px;
  left: 50%;
  transform: translateX(-50%);
  display: flex;
  align-items: center;
  gap: 18px;
  color: #7f8a86;
  font-size: 10px;
  font-weight: 800;
}

.application {
  position: relative;
}

.application::before {
  content: "";
  display: inline-block;
  width: 5px;
  height: 5px;
  margin-right: 5px;
  border: 1px solid currentColor;
  border-radius: 50%;
  vertical-align: 1px;
}

.application.is-active {
  color: var(--reflected);
}

.application.is-active::before {
  background: currentColor;
}

.principle-band {
  position: absolute;
  left: 50%;
  bottom: calc(max(100px, env(safe-area-inset-bottom) + 92px));
  width: min(760px, calc(100% - 44px));
  min-height: 42px;
  transform: translateX(-50%);
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 24px;
  padding: 8px 16px;
  border-top: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  background: rgba(8, 12, 13, 0.48);
  backdrop-filter: blur(8px);
  font-size: 14px;
  font-weight: 850;
  text-align: center;
}

#law-text {
  color: var(--normal);
  font-family: "Cambria Math", Georgia, serif;
}

.control-dock {
  position: absolute;
  left: 50%;
  bottom: max(18px, env(safe-area-inset-bottom));
  width: min(1180px, calc(100% - 32px));
  min-height: 64px;
  transform: translateX(-50%);
  display: grid;
  grid-template-columns: auto auto auto minmax(160px, 1fr) minmax(160px, 1fr) auto auto;
  align-items: center;
  gap: 9px;
  padding: 8px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--panel);
  box-shadow: 0 12px 36px rgba(0, 0, 0, 0.34);
  backdrop-filter: blur(14px);
  pointer-events: auto;
}

.control-btn,
.segmented button {
  height: 44px;
  border: 1px solid rgba(255, 255, 255, 0.13);
  border-radius: 6px;
  background: rgba(255, 255, 255, 0.055);
  color: var(--ink);
  cursor: pointer;
  transition: border-color 140ms ease, background 140ms ease, color 140ms ease;
}

.control-btn:hover,
.segmented button:hover {
  border-color: rgba(255, 255, 255, 0.3);
  background: rgba(255, 255, 255, 0.1);
}

.control-btn:focus-visible,
.segmented button:focus-visible,
input[type="range"]:focus-visible {
  outline: 2px solid var(--ink);
  outline-offset: 2px;
}

.control-btn.primary {
  min-width: 104px;
  padding: 0 18px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  border-color: rgba(255, 181, 46, 0.5);
  background: var(--reflected);
  color: #171108;
  font-weight: 900;
}

.button-icon {
  width: 14px;
  text-align: center;
}

.control-btn.icon-only {
  width: 44px;
  padding: 0;
  font-size: 20px;
  line-height: 1;
}

.segmented {
  display: grid;
  grid-template-columns: repeat(2, minmax(54px, 1fr));
  gap: 3px;
  padding: 3px;
  border: 1px solid var(--line);
  border-radius: 7px;
}

.segmented button {
  height: 34px;
  padding: 0 10px;
  border-color: transparent;
  font-size: 12px;
  font-weight: 850;
}

.segmented button.is-active {
  background: rgba(45, 212, 191, 0.14);
  color: var(--mirror);
}

.direction-control button.is-active {
  background: rgba(255, 181, 46, 0.15);
  color: var(--reflected);
}

.slider-control {
  min-width: 0;
  display: grid;
  grid-template-columns: 82px minmax(80px, 1fr);
  align-items: center;
  gap: 8px;
  padding: 0 6px;
  color: var(--muted);
  font-size: 10px;
  font-weight: 750;
}

.slider-control span {
  white-space: nowrap;
}

.slider-control b {
  color: var(--ink);
  font-variant-numeric: tabular-nums;
}

input[type="range"] {
  width: 100%;
  min-width: 0;
  height: 20px;
  margin: 0;
  appearance: none;
  background: transparent;
  cursor: pointer;
}

input[type="range"]::-webkit-slider-runnable-track {
  height: 4px;
  border-radius: 2px;
  background: rgba(255, 255, 255, 0.17);
}

input[type="range"]::-webkit-slider-thumb {
  width: 18px;
  height: 18px;
  margin-top: -7px;
  appearance: none;
  border: 3px solid var(--bg);
  border-radius: 50%;
  background: var(--mirror);
  box-shadow: 0 0 0 1px rgba(45, 212, 191, 0.72);
}

.angle-control input[type="range"]::-webkit-slider-thumb {
  background: var(--incoming);
  box-shadow: 0 0 0 1px rgba(255, 241, 184, 0.72);
}

input[type="range"]::-moz-range-track {
  height: 4px;
  background: rgba(255, 255, 255, 0.17);
}

input[type="range"]::-moz-range-thumb {
  width: 14px;
  height: 14px;
  border: 3px solid var(--bg);
  border-radius: 50%;
  background: var(--mirror);
}

.fullscreen-button {
  z-index: 8 !important;
  top: max(12px, env(safe-area-inset-top)) !important;
  right: 12px !important;
  opacity: 0.72;
}

@media (max-width: 980px) {
  .lesson-header {
    width: calc(100% - 76px);
    grid-template-columns: minmax(220px, 0.8fr) minmax(430px, 1.4fr);
  }

  .control-dock {
    grid-template-columns: auto auto auto minmax(140px, 1fr) minmax(140px, 1fr) auto;
  }

  #btn-view {
    display: none;
  }
}

@media (max-width: 640px) {
  .lesson-header {
    top: max(8px, env(safe-area-inset-top));
    width: calc(100% - 64px);
    display: block;
    padding: 7px 8px;
  }

  .eyebrow {
    margin-bottom: 3px;
    font-size: 7px;
  }

  h1 {
    font-size: 24px;
  }

  .subtitle {
    margin-top: 3px;
    font-size: 10px;
  }

  .value-board {
    grid-template-columns: 1.2fr repeat(3, minmax(0, 1fr));
    margin-top: 7px;
  }

  .value-item {
    padding: 6px 5px;
  }

  .value-item span {
    font-size: 7px;
  }

  .value-item strong {
    font-size: 11px;
  }

  .story-caption {
    top: 137px;
    min-width: calc(100% - 28px);
    grid-template-columns: 28px auto;
    padding: 6px 10px;
  }

  .caption-step {
    font-size: 19px;
  }

  .story-caption strong {
    font-size: 12px;
  }

  .story-caption > span:last-child {
    font-size: 8px;
  }

  .application-strip {
    top: 183px;
    gap: 12px;
    font-size: 8px;
  }

  .principle-band {
    bottom: calc(max(146px, env(safe-area-inset-bottom) + 138px));
    width: calc(100% - 28px);
    min-height: 38px;
    flex-direction: column;
    gap: 2px;
    padding: 6px 8px;
    font-size: 10px;
  }

  .control-dock {
    bottom: max(9px, env(safe-area-inset-bottom));
    width: calc(100% - 18px);
    min-height: 126px;
    grid-template-columns: 74px 1fr 1fr 38px;
    grid-template-rows: 44px 30px 30px;
    gap: 4px;
    padding: 6px;
  }

  .control-btn.primary {
    min-width: 0;
    height: 44px;
    padding: 0 8px;
    font-size: 12px;
  }

  .direction-control,
  .beam-control {
    min-width: 0;
  }

  .segmented button {
    height: 34px;
    padding: 0 4px;
    font-size: 10px;
  }

  #btn-view {
    display: none;
  }

  .control-btn.icon-only {
    width: 38px;
    height: 44px;
  }

  .focus-control,
  .angle-control {
    grid-column: 1 / -1;
    grid-template-columns: 74px minmax(0, 1fr);
    height: 30px;
    padding: 0 4px;
  }

  .focus-control { grid-row: 2; }
  .angle-control { grid-row: 3; }

  .slider-control {
    font-size: 9px;
  }
}

@media (max-height: 620px) and (min-width: 641px) {
  .lesson-header {
    top: 8px;
    padding-top: 6px;
    padding-bottom: 6px;
  }

  .subtitle,
  .application-strip {
    display: none;
  }

  .story-caption {
    top: 94px;
  }

  .principle-band {
    bottom: 84px;
  }

  .control-dock {
    bottom: 10px;
  }
}

@media (prefers-reduced-motion: reduce) {
  * {
    transition-duration: 0.01ms !important;
  }
}