:root {
  --brand-blue: #2563eb;
  --brand-indigo: #4f46e5;
  --brand-amber: #f59e0b;
  --brand-green: #16a34a;
  --brand-red: #dc2626;
  --bg-soft: #f5f7fb;
}

* {
  box-sizing: border-box;
}

html, body {
  font-family: 'Noto Sans TC', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  background: var(--bg-soft);
  margin: 0;
  color: #1e293b;
}

.loading-screen {
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100vh;
  font-size: 1.5rem;
  color: var(--brand-blue);
}

/* ---------- Navbar ---------- */
.navbar {
  background: linear-gradient(135deg, var(--brand-blue), var(--brand-indigo));
  color: white;
  box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}

/* ---------- Level Card ---------- */
.level-card {
  transition: transform 0.2s ease, box-shadow 0.2s ease;
}
.level-card:hover {
  transform: translateY(-4px);
  box-shadow: 0 12px 24px rgba(37,99,235,0.15);
}

.chapter-card {
  transition: transform 0.15s ease, box-shadow 0.15s ease;
  border-left: 5px solid transparent;
}
.chapter-card:hover {
  transform: translateY(-3px);
  box-shadow: 0 10px 20px rgba(0,0,0,0.08);
}
.chapter-card.type-2d { border-left-color: var(--brand-blue); }
.chapter-card.type-3d { border-left-color: var(--brand-amber); }

/* ---------- Canvas containers ---------- */
.canvas-wrap {
  background: #ffffff;
  border-radius: 12px;
  border: 1px solid #e2e8f0;
  position: relative;
  overflow: hidden;
}

canvas {
  display: block;
  touch-action: none;
}

.slider-row {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin-bottom: 0.5rem;
}
.slider-row label {
  min-width: 90px;
  font-weight: 600;
  color: #334155;
  font-size: 0.9rem;
}
.slider-row input[type=range] {
  flex: 1;
  accent-color: var(--brand-blue);
}
.slider-value {
  min-width: 60px;
  text-align: right;
  font-family: monospace;
  color: var(--brand-indigo);
  font-weight: 700;
}

/* ---------- Progress bar ---------- */
.mastery-bar-bg {
  background: #e2e8f0;
  border-radius: 999px;
  height: 10px;
  overflow: hidden;
}
.mastery-bar-fill {
  height: 100%;
  border-radius: 999px;
  background: linear-gradient(90deg, #22c55e, #16a34a);
  transition: width 0.5s ease;
}

.badge-pill {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  padding: 3px 10px;
  border-radius: 999px;
  background: #fef3c7;
  color: #92400e;
  font-size: 0.75rem;
  font-weight: 700;
}

/* ---------- Option buttons ---------- */
.option-btn {
  display: block;
  width: 100%;
  text-align: left;
  padding: 12px 16px;
  border: 2px solid #e2e8f0;
  border-radius: 10px;
  background: white;
  margin-bottom: 10px;
  cursor: pointer;
  transition: all 0.15s ease;
  font-size: 1rem;
}
.option-btn:hover {
  border-color: var(--brand-blue);
  background: #eff6ff;
}
.option-btn.selected {
  border-color: var(--brand-blue);
  background: #dbeafe;
}
.option-btn.correct {
  border-color: var(--brand-green);
  background: #dcfce7;
}
.option-btn.wrong {
  border-color: var(--brand-red);
  background: #fee2e2;
}
.option-btn:disabled {
  cursor: default;
}

.spin {
  animation: spin 1s linear infinite;
}
@keyframes spin {
  from { transform: rotate(0deg); }
  to { transform: rotate(360deg); }
}

.fade-in {
  animation: fadeIn 0.3s ease;
}
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: translateY(0); }
}

.tab-btn {
  padding: 8px 18px;
  border-radius: 999px;
  font-weight: 700;
  cursor: pointer;
  transition: all 0.15s ease;
}
.tab-btn.active {
  background: var(--brand-blue);
  color: white;
}
.tab-btn:not(.active) {
  background: #e2e8f0;
  color: #475569;
}

.katex-display {
  margin: 0.3em 0 !important;
}