:root { --bg: #f5f7fa; --fg: #333; --card-bg: #fff; --card-border: #e0e0e0; --primary: #3949ab; --primary-hover: #303f9f; --primary-bg: #e8eaf6; --success: #43a047; --success-bg: #e8f5e9; --danger: #e53935; --danger-bg: #ffebee; --muted: #888; --muted-text: #666; --diagram-bg: #f8f9fa; --heading: #1a237e; --welcome-sub: #666; --toast-bg: #1a237e; --stat-shadow: rgba(0,0,0,0.1); --topic-bar-bg: #e0e0e0; }
[data-theme="dark"] { --bg: #121212; --fg: #e0e0e0; --card-bg: #1e1e1e; --card-border: #333; --primary: #5c6bc0; --primary-hover: #7986cb; --primary-bg: #283593; --success-bg: #1b5e20; --danger-bg: #b71c1c; --muted: #999; --muted-text: #aaa; --diagram-bg: #2a2a2a; --heading: #9fa8da; --welcome-sub: #999; --toast-bg: #37474f; --stat-shadow: rgba(0,0,0,0.3); --topic-bar-bg: #444; }
[data-theme="high-contrast"] { --bg: #fff; --fg: #000; --card-bg: #fff; --card-border: #000; --primary: #000; --primary-hover: #333; --primary-bg: #e0e0e0; --success-bg: #c8e6c9; --danger-bg: #ffcdd2; --muted: #000; --muted-text: #000; --heading: #000; --welcome-sub: #000; --toast-bg: #000; --topic-bar-bg: #999; }
* { box-sizing: border-box; margin: 0; padding: 0; }
body { font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif; background: var(--bg); color: var(--fg); transition: background 0.2s, color 0.2s; }
.container { max-width: 720px; margin: 0 auto; padding: 16px; min-height: 100vh; display: flex; flex-direction: column; }
.hidden { display: none !important; }
h1 { font-size: 1.5rem; margin-bottom: 8px; color: var(--heading); }
h2 { font-size: 1.2rem; margin-bottom: 12px; color: var(--heading); }
p { margin-bottom: 12px; line-height: 1.5; }

.btn { display: inline-block; padding: 12px 24px; border: none; border-radius: 8px; font-size: 1rem; cursor: pointer; font-weight: 600; transition: background 0.2s; }
.btn-primary { background: var(--primary); color: #fff; }
.btn-primary:hover { background: var(--primary-hover); }
.btn-success { background: var(--success); color: #fff; }
.btn-outline { background: transparent; border: 2px solid var(--primary); color: var(--primary); }
.btn-sm { padding: 6px 12px; font-size: 0.8rem; }
.toast { position: fixed; bottom: 20px; left: 50%; transform: translateX(-50%); background: var(--toast-bg); color: #fff; padding: 12px 24px; border-radius: 8px; font-weight: 600; font-size: 0.9rem; box-shadow: 0 4px 12px rgba(0,0,0,0.2); transition: opacity 0.3s; opacity: 0; pointer-events: none; z-index: 100; }
.toast.show { opacity: 1; }

.welcome-header { text-align: center; padding: 40px 0 24px; }
.welcome-header .subtitle { color: var(--welcome-sub); font-size: 0.95rem; }
.stats-row { display: flex; gap: 12px; margin: 20px 0; }
.stat-card { flex: 1; background: var(--card-bg); border-radius: 10px; padding: 16px; text-align: center; box-shadow: 0 1px 3px var(--stat-shadow); }
.stat-card .stat-num { font-size: 1.8rem; font-weight: 700; color: var(--heading); }
.stat-card .stat-label { font-size: 0.75rem; color: var(--muted); text-transform: uppercase; letter-spacing: 0.5px; }

.topic-row { display: flex; align-items: center; gap: 8px; margin: 6px 0; font-size: 0.85rem; }
.topic-row span:first-child { width: 140px; text-align: right; white-space: nowrap; }
.topic-bar { flex: 1; height: 12px; background: var(--topic-bar-bg); border-radius: 6px; overflow: hidden; }
.topic-fill { height: 100%; background: linear-gradient(90deg, #42a5f5, var(--primary)); border-radius: 6px; transition: width 0.5s; }
.mastered-fill { background: linear-gradient(90deg, #f9a825, #f57f17); }
.topic-pct { width: 40px; font-weight: 600; color: var(--muted-text); }

.card-header { display: flex; justify-content: space-between; font-size: 0.85rem; color: var(--muted-text); margin-bottom: 8px; }
.card-meta { display: flex; gap: 12px; }
.card-prerequisites { margin: 8px 0; padding: 8px 10px; border-left: 3px solid var(--primary); background: var(--primary-bg); border-radius: 0 6px 6px 0; color: var(--fg); font-size: 0.8rem; }
#scenario { background: var(--card-bg); border-radius: 10px; padding: 16px; margin: 8px 0; line-height: 1.6; box-shadow: 0 1px 3px var(--stat-shadow); font-size: 0.95rem; }
#diagram-container { margin: 8px 0; background: var(--diagram-bg); border-radius: 10px; padding: 8px; min-height: 140px; box-shadow: 0 1px 3px var(--stat-shadow); }
#options { display: flex; flex-direction: column; gap: 8px; margin: 12px 0; }
.option-btn { display: flex; align-items: center; gap: 12px; padding: 14px 16px; border: 2px solid var(--card-border); border-radius: 10px; background: var(--card-bg); cursor: pointer; font-size: 0.9rem; text-align: left; transition: all 0.15s; }
.option-btn:hover:not(:disabled) { border-color: var(--primary); background: var(--primary-bg); }
.option-btn:disabled { cursor: default; opacity: 0.85; }
.option-btn.correct { border-color: var(--success); background: var(--success-bg); }
.option-btn.incorrect { border-color: var(--danger); background: var(--danger-bg); }
.option-letter { display: inline-flex; align-items: center; justify-content: center; width: 28px; height: 28px; border-radius: 50%; background: var(--primary-bg); font-weight: 700; font-size: 0.85rem; color: var(--primary); flex-shrink: 0; }
.option-btn.correct .option-letter { background: var(--success); color: #fff; }
.option-btn.incorrect .option-letter { background: var(--danger); color: #fff; }
.option-text { flex: 1; }

#feedback { background: var(--card-bg); border-radius: 10px; padding: 16px; margin: 8px 0; line-height: 1.6; font-size: 0.9rem; border-left: 4px solid; }
#feedback.correct { border-color: var(--success); }
#feedback.incorrect { border-color: var(--danger); }
.post-answer-actions { margin: 10px 0; padding: 10px; background: var(--bg); }
#confidence-buttons p { margin: 0 0 8px; text-align: center; color: var(--muted-text); font-size: 0.85rem; font-weight: 600; }
.confidence-options { display: grid; grid-template-columns: repeat(4, minmax(0, 1fr)); gap: 6px; }
.confidence-options .btn { min-width: 0; padding: 9px 4px; }
#quality-rating { display: flex; gap: 8px; justify-content: center; margin: 8px 0; }
#quality-rating span { align-self: center; color: var(--muted); font-size: 0.8rem; }
.next-card-actions { display: flex; gap: 8px; margin-top: 8px; }
#next-btn { flex: 1; }
#regenerate-btn { flex: 0 0 auto; padding: 10px 14px; }
.keyboard-hint { font-size: 0.7rem; opacity: 0.6; }

#session-summary p { margin: 8px 0; font-size: 1.05rem; }
.actions { display: flex; gap: 12px; margin-top: 20px; flex-wrap: wrap; }
.actions .btn { flex: 1; text-align: center; }

@media (prefers-reduced-motion) { *, *::before, *::after { transition: none !important; } }
.heatmap { display: grid; grid-template-columns: repeat(auto-fill, 28px); gap: 4px; margin: 12px 0; }
.heatmap-cell { width: 28px; height: 28px; border-radius: 4px; font-size: 0.6rem; display: flex; align-items: center; justify-content: center; font-weight: 600; }
.heatmap-label { font-size: 0.65rem; color: var(--muted); grid-column: 1 / -1; margin-top: 4px; }
.screen-intro { color: var(--muted-text); font-size: 0.9rem; }
.prerequisite-fieldset { border: 1px solid var(--card-border); border-radius: 8px; padding: 10px; }
.prerequisite-fieldset legend { padding: 0 4px; color: var(--muted-text); font-size: 0.85rem; }
.prerequisite-options { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 6px 12px; }
.prerequisite-option { display: flex; align-items: center; gap: 6px; min-width: 0; font-size: 0.8rem; }
.prerequisite-option input { width: 16px; height: 16px; accent-color: var(--primary); flex: 0 0 auto; }
.topic-level { margin: 18px 0 24px; }
.topic-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 10px; }
.topic-node { min-width: 0; padding: 12px; border: 1px solid var(--card-border); border-radius: 8px; background: var(--card-bg); }
.topic-node-heading { display: flex; justify-content: space-between; align-items: baseline; gap: 8px; }
.topic-node-heading span { color: var(--muted); font-size: 0.75rem; }
.topic-node-progress { height: 6px; margin: 8px 0; overflow: hidden; background: var(--topic-bar-bg); border-radius: 3px; }
.topic-node-progress span { display: block; height: 100%; background: var(--primary); }
.topic-node p { margin: 4px 0; color: var(--muted-text); font-size: 0.75rem; }
.topic-node .btn { width: 100%; margin-top: 8px; padding: 7px; }
@media (max-width: 480px) {
  .stats-row { flex-direction: column; }
  .topic-row span:first-child { width: 100px; }
  .topic-grid, .prerequisite-options { grid-template-columns: 1fr; }
  .card-header { align-items: flex-start; gap: 6px; }
  .card-meta { flex-wrap: wrap; justify-content: flex-end; gap: 6px; }
  .post-answer-actions:not(.hidden) { position: sticky; bottom: 0; z-index: 10; margin: 8px -16px -16px; padding: 10px 16px calc(10px + env(safe-area-inset-bottom)); border-top: 1px solid var(--card-border); box-shadow: 0 -4px 12px var(--stat-shadow); }
  .keyboard-hint { display: none; }
}