:root {
  --paper: #f7f5ef;
  --paper-deep: #ece9df;
  --ink: #1f2937;
  --muted: #667085;
  --line: #d8ddd9;
  --mint: #41c7bb;
  --mint-soft: #e0f4f0;
  --coral: #d9695e;
  --coral-soft: #fce8e4;
}

* { box-sizing: border-box; -webkit-tap-highlight-color: transparent; }
[hidden] { display: none !important; }

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

button, select { font: inherit; }

.ui-loading {
  position: fixed;
  top: 18px;
  left: 50%;
  z-index: 30;
  padding: 8px 13px;
  border: 1px solid var(--line);
  border-radius: 5px;
  background: rgba(255, 255, 255, .92);
  color: var(--muted);
  font-size: 12px;
  transform: translateX(-50%);
  transition: opacity .3s ease, visibility .3s ease;
}

.ui-loading.is-done { opacity: 0; visibility: hidden; }

#lesson-shell,
#lesson-viewport,
#v3d-container,
#cube-render-host {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
}

#lesson-viewport { overflow: hidden; background: var(--paper); }
#cube-render-host { z-index: 1; }
#cube-render-host canvas { display: block; width: 100%; height: 100%; outline: none; cursor: grab; touch-action: none; }
#cube-render-host canvas.is-dragging { cursor: grabbing; }
#cube-render-host canvas.is-choice-hover { cursor: pointer; }

.viewport-header {
  position: absolute;
  top: 25px;
  left: 30px;
  z-index: 4;
  pointer-events: none;
}

.eyebrow, .panel-kicker { color: var(--mint); font-size: 11px; font-weight: 800; }
.viewport-header h1 { margin: 6px 0 0; font-family: "STKaiti", "KaiTi", serif; font-size: 34px; letter-spacing: 0; }
.viewport-note { margin-top: 7px; color: var(--muted); font-size: 11px; }

.step-readout {
  position: absolute;
  right: 30px;
  top: 28px;
  z-index: 4;
  display: flex;
  align-items: baseline;
  gap: 9px;
  color: var(--muted);
  font-size: 12px;
  pointer-events: none;
}

.step-readout strong { color: var(--ink); font-size: 19px; }

#lesson-panel {
  position: absolute;
  left: 50%;
  bottom: 18px;
  z-index: 12;
  width: min(1000px, calc(100% - 40px));
  padding: 9px 14px 11px;
  border: 1px solid rgba(31, 41, 55, .13);
  border-radius: 7px;
  background: rgba(255, 255, 255, .94);
  box-shadow: 0 10px 30px rgba(31, 41, 55, .13);
  transform: translateX(-50%);
  transition: opacity .24s ease, transform .28s ease, visibility .28s ease;
  backdrop-filter: blur(10px);
}

body.ui-hidden #lesson-panel { opacity: .15; pointer-events: none; }
body.ui-collapsed #lesson-panel { opacity: 0; visibility: hidden; transform: translate(-50%, calc(100% + 36px)); }
body.ui-collapsed .viewport-header,
body.ui-collapsed .step-readout { opacity: 0; visibility: hidden; }

.panel-topline { display: flex; align-items: center; justify-content: space-between; gap: 16px; min-height: 34px; padding-bottom: 7px; border-bottom: 1px solid var(--line); }
.panel-title-group { display: flex; align-items: center; gap: 10px; min-width: 0; }
body:not(.is-setting):not(.is-turn-setting) .panel-title-group { display: none; }
.panel-topline h2 { margin: 0; font-size: 17px; line-height: 1.25; white-space: nowrap; }
.panel-actions { display: flex; gap: 7px; margin-left: auto; }

.icon-button {
  min-width: 58px;
  min-height: 34px;
  padding: 6px 10px;
  border: 1px solid var(--line);
  border-radius: 5px;
  background: #fff;
  color: var(--ink);
  cursor: pointer;
  font-size: 12px;
  font-weight: 750;
}
.icon-button:hover { border-color: var(--mint); background: var(--mint-soft); }
.icon-button:disabled { opacity: .42; cursor: not-allowed; }

.normal-content { display: grid; grid-template-columns: 1.08fr 1fr 1.16fr; gap: 18px; align-items: start; padding-top: 10px; }
.question-block, .answer-panel, .controls { min-width: 0; }
.question-block { padding-right: 6px; border-right: 1px solid rgba(31, 41, 55, .12); }
.face-relation { display: flex; flex-direction: column; align-items: stretch; gap: 6px; min-height: 111px; color: var(--muted); font-size: 12px; }
.face-relation > span { font-weight: 800; }
.face-relation strong { display: flex; align-items: center; justify-content: center; min-height: 27px; padding: 3px 8px; border-radius: 4px; background: var(--paper-deep); color: var(--ink); font-size: 16px; line-height: 1; }

.answer-label, .control-heading, .explanation-title { color: var(--ink); font-size: 12px; font-weight: 800; }
.answer-options { display: grid; grid-template-columns: repeat(6, 1fr); gap: 5px; margin-top: 7px; }
.answer-option {
  min-width: 0;
  min-height: 35px;
  border: 1px solid var(--line);
  border-radius: 4px;
  background: #fff;
  color: var(--ink);
  cursor: pointer;
  font-size: 15px;
  font-weight: 800;
}
.answer-option:hover { border-color: var(--mint); }
.answer-option.is-selected { border-color: var(--mint); background: var(--mint-soft); color: #1b716b; box-shadow: inset 0 0 0 1px var(--mint); }

.primary-button, .secondary-button { min-height: 35px; border-radius: 4px; cursor: pointer; font-size: 12px; font-weight: 800; }
.primary-button { width: 100%; margin-top: 6px; border: 1px solid var(--ink); background: var(--ink); color: #fff; }
.primary-button:hover { background: #354354; }
.primary-button.is-answer-correct { border-color: #2d9f72; background: #2d9f72; }
.primary-button.is-answer-wrong { border-color: #cf6262; background: #cf6262; animation: answer-wrong-shake .32s ease-in-out; }
.primary-button:disabled, .secondary-button:disabled { opacity: .42; cursor: not-allowed; }

@keyframes answer-wrong-shake {
  0%, 100% { transform: translateX(0); }
  25% { transform: translateX(-2px); }
  75% { transform: translateX(2px); }
}

.control-heading { display: flex; justify-content: space-between; }
.control-heading span:last-child { color: var(--muted); font-size: 10px; }
.control-buttons { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 6px; margin-top: 7px; }
.secondary-button { display: inline-flex; align-items: center; justify-content: center; gap: 5px; min-width: 0; border: 1px solid var(--line); background: #fff; color: var(--ink); padding: 0 9px; white-space: nowrap; }
.secondary-button:hover, .secondary-button.is-active { border-color: var(--mint); background: var(--mint-soft); }
.button-icon { color: var(--mint); }

.feedback { display: none; }
.feedback.is-good { border-color: #2d9f72; background: #e4f5ec; }
.feedback.is-bad { border-color: var(--coral); background: var(--coral-soft); }
.feedback-title { font-size: 12px; font-weight: 800; }
.feedback-text { margin-top: 4px; color: var(--muted); font-size: 11px; line-height: 1.45; }
.setup-content { display: grid; grid-template-columns: auto 1fr; align-items: center; gap: 18px; padding-top: 12px; }
.setup-content > div { display: flex; flex-direction: column; gap: 4px; }
.setup-content strong { font-size: 14px; }
.setup-content span, .setup-content p { color: var(--muted); font-size: 11px; }
.setup-content p { margin: 0; line-height: 1.5; }
.setup-content > .turn-choice-buttons { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 8px; width: min(450px, 100%); }
.turn-choice-button {
  display: grid;
  grid-template-columns: 42px minmax(0, 1fr);
  align-items: center;
  gap: 5px;
  min-height: 50px;
  padding: 4px 9px 4px 4px;
  border: 1px solid var(--line);
  border-radius: 5px;
  background: #fff;
  color: var(--ink);
  cursor: pointer;
  font-size: 11px;
  font-weight: 800;
  text-align: left;
}
.turn-choice-button:hover { border-color: var(--mint); background: var(--mint-soft); }
.turn-choice-button.is-selected { border-color: var(--mint); background: var(--mint-soft); box-shadow: inset 0 0 0 1px var(--mint); }
.turn-choice-button canvas { display: block; width: 42px; height: 42px; }

.face-picker {
  position: absolute;
  z-index: 20;
  display: flex;
  align-items: center;
  gap: 7px;
  padding: 8px;
  border: 1px solid rgba(31, 41, 55, .17);
  border-radius: 5px;
  background: #fff;
  box-shadow: 0 8px 22px rgba(31, 41, 55, .18);
  color: var(--muted);
  font-size: 11px;
}
.face-picker[hidden] { display: none; }
.face-picker select { min-width: 64px; min-height: 34px; padding: 4px 7px; border: 1px solid var(--line); border-radius: 4px; background: #fff; color: var(--ink); font-weight: 800; }

.floating-ui-button {
  position: absolute;
  left: 50%;
  bottom: 18px;
  z-index: 14;
  display: none;
  min-height: 40px;
  padding: 0 17px;
  border: 1px solid var(--ink);
  border-radius: 5px;
  background: var(--ink);
  color: #fff;
  font-size: 12px;
  font-weight: 800;
  transform: translateX(-50%);
  cursor: pointer;
}
body.ui-collapsed .floating-ui-button { display: block; }

body.is-setting .viewport-header,
body.is-setting .step-readout,
body.is-turn-setting .viewport-header,
body.is-turn-setting .step-readout { opacity: 0; visibility: hidden; }
body.is-setting #lesson-panel,
body.is-turn-setting #lesson-panel { width: min(720px, calc(100% - 40px)); }
body.is-setting .panel-kicker { display: none; }

button:focus-visible, select:focus-visible { outline: 3px solid rgba(65,199,187,.35); outline-offset: 2px; }

@media (max-width: 760px) {
  .viewport-header { top: 16px; left: 18px; }
  .viewport-header h1 { font-size: 27px; }
  .viewport-note { display: none; }
  .step-readout { top: 18px; right: 18px; }
  #lesson-panel { bottom: 8px; width: calc(100% - 16px); max-height: 47vh; overflow-y: auto; padding: 12px; }
  .panel-topline { align-items: flex-start; }
  .panel-title-group { display: block; }
  .panel-topline h2 { margin-top: 3px; font-size: 15px; white-space: normal; }
  .panel-actions { flex-shrink: 0; }
  .normal-content { grid-template-columns: 1fr 1fr; gap: 11px; }
  .setup-content { grid-template-columns: 1fr; gap: 6px; }
  .setup-content > .turn-choice-buttons { width: 100%; }
  .floating-ui-button { bottom: 10px; }
}

@media (max-width: 430px) {
  .normal-content { grid-template-columns: 1fr; }
  .answer-option { min-height: 38px; }
  .secondary-button { min-height: 38px; }
  .setup-content > .turn-choice-buttons { grid-template-columns: 1fr; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { transition-duration: .01ms !important; animation-duration: .01ms !important; }
}