:root {
  --body-bg: #f8f9fa;
  --text-color: #1a1a2e;
  --text-secondary: #666;
  --card-bg: #fff;
  --input-bg: #f5f5f5;
  --border-color: #e5e7eb;
  --correct-bg: #dcfce7;
  --correct-text: #166534;
  --correct-border: #86efac;
  --wrong-bg: #fee2e2;
  --wrong-text: #991b1b;
  --wrong-border: #fca5a5;
  --progress-bg: #e5e7eb;
  --hover-bg: #eef2ff;
  --code-bg: #1e1e2e;
  --code-text: #cdd6f4;
}

@media (prefers-color-scheme: dark) {
  :root {
    --body-bg: #0f111a;
    --text-color: #e2e8f0;
    --text-secondary: #94a3b8;
    --card-bg: #1e2030;
    --input-bg: #282a3a;
    --border-color: #334155;
    --correct-bg: #052e16;
    --correct-text: #86efac;
    --correct-border: #166534;
    --wrong-bg: #450a0a;
    --wrong-text: #fca5a5;
    --wrong-border: #991b1b;
    --progress-bg: #334155;
    --hover-bg: #1e1b4b;
    --code-bg: #11111b;
    --code-text: #cdd6f4;
  }
}

* { box-sizing: border-box; margin: 0; padding: 0; }

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', system-ui, sans-serif;
  line-height: 1.6;
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
}

/* Cards */
.card {
  background: var(--card-bg);
  border: 1px solid var(--border-color);
  border-radius: 12px;
  padding: 20px;
  transition: box-shadow 0.2s ease;
}

/* Option buttons */
.option-btn {
  width: 100%;
  text-align: left;
  padding: 14px 16px;
  border-radius: 10px;
  border: 1.5px solid var(--border-color);
  background: var(--card-bg);
  color: var(--text-color);
  font-size: 15px;
  line-height: 1.5;
  cursor: pointer;
  transition: all 0.15s ease;
  min-height: 48px;
}
.option-btn:hover:not(:disabled) {
  background: var(--hover-bg);
  border-color: #6366f1;
}
.option-btn:disabled { cursor: default; opacity: 0.85; }
.option-btn.correct {
  background: var(--correct-bg);
  border-color: var(--correct-border);
  color: var(--correct-text);
}
.option-btn.wrong {
  background: var(--wrong-bg);
  border-color: var(--wrong-border);
  color: var(--wrong-text);
}

/* Progress bar */
.progress-track {
  height: 6px;
  background: var(--progress-bg);
  border-radius: 3px;
  overflow: hidden;
}
.progress-fill {
  height: 100%;
  border-radius: 3px;
  transition: width 0.4s ease;
}

/* Badge */
.badge {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  padding: 3px 10px;
  border-radius: 20px;
  font-size: 12px;
  font-weight: 600;
  line-height: 1.4;
}

/* Tag badge */
.tag-badge {
  display: inline-flex;
  align-items: center;
  padding: 2px 8px;
  border-radius: 6px;
  font-size: 11px;
  font-weight: 500;
  background: var(--input-bg);
  color: var(--text-secondary);
  border: 1px solid var(--border-color);
}

/* Speak button */
.speak-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 32px;
  height: 32px;
  border-radius: 50%;
  border: 1px solid var(--border-color);
  background: var(--input-bg);
  cursor: pointer;
  font-size: 16px;
  transition: all 0.15s ease;
  flex-shrink: 0;
}
.speak-btn:hover { background: var(--hover-bg); }
.speak-btn:active { transform: scale(0.92); }

/* Primary button */
.btn-primary {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  padding: 12px 24px;
  border-radius: 10px;
  border: none;
  background: #6366f1;
  color: #fff;
  font-size: 15px;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.15s ease;
  min-height: 44px;
}
.btn-primary:hover { background: #4f46e5; }
.btn-primary:active { transform: scale(0.97); }
.btn-primary:disabled { opacity: 0.5; cursor: not-allowed; }

/* Secondary button */
.btn-secondary {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  padding: 12px 24px;
  border-radius: 10px;
  border: 1.5px solid var(--border-color);
  background: var(--card-bg);
  color: var(--text-color);
  font-size: 15px;
  font-weight: 500;
  cursor: pointer;
  transition: all 0.15s ease;
  min-height: 44px;
}
.btn-secondary:hover { border-color: #6366f1; background: var(--hover-bg); }

/* Ghost button (skip) */
.btn-ghost {
  padding: 8px 16px;
  border: none;
  background: none;
  color: var(--text-secondary);
  font-size: 13px;
  cursor: pointer;
  transition: color 0.15s;
}
.btn-ghost:hover { color: var(--text-color); }

/* Term card */
.term-card {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  padding: 12px;
  border-radius: 10px;
  background: var(--input-bg);
}

/* Callout */
.callout {
  padding: 16px;
  border-radius: 10px;
  background: var(--input-bg);
  border-left: 3px solid #f59e0b;
}

/* Context block — for architect quiz situational description */
.context-block {
  padding: 16px;
  border-radius: 10px;
  background: var(--input-bg);
  border-left: 3px solid #6366f1;
}

/* Explanation sections */
.explanation-section {
  background: var(--card-bg);
  border: 1px solid var(--border-color);
  border-radius: 12px;
  padding: 16px;
}

/* Variant explanation blocks */
.variant-explanation {
  padding: 12px;
  border-radius: 8px;
  background: var(--input-bg);
}
.variant-correct {
  border-left: 3px solid #16a34a;
}
.variant-other {
  border-left: 3px solid var(--border-color);
}

/* Code block for examples */
.code-block {
  background: var(--code-bg);
  color: var(--code-text);
  padding: 16px;
  border-radius: 8px;
  overflow-x: auto;
  font-family: 'Fira Code', 'Cascadia Code', 'JetBrains Mono', 'Consolas', monospace;
  font-size: 12px;
  line-height: 1.6;
  white-space: pre;
  -webkit-overflow-scrolling: touch;
  max-height: 400px;
}

/* Weak topic warning card */
.weak-topic-card {
  background: #dc262608;
  border: 1px solid #dc262633;
  border-radius: 12px;
  padding: 16px;
}

/* Random input */
.random-input {
  width: 100%;
  padding: 12px 16px;
  border-radius: 10px;
  border: 1.5px solid var(--border-color);
  background: var(--input-bg);
  color: var(--text-color);
  font-size: 16px;
  outline: none;
  transition: border-color 0.15s;
}
.random-input:focus {
  border-color: #6366f1;
}

/* Category card */
.category-card {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 14px 16px;
  border-radius: 10px;
  border: 1.5px solid var(--border-color);
  background: var(--card-bg);
  cursor: pointer;
  transition: all 0.15s ease;
  min-height: 48px;
}
.category-card:hover {
  border-color: #6366f1;
  background: var(--hover-bg);
}

/* Stat bar */
.stat-bar {
  height: 8px;
  border-radius: 4px;
  background: var(--progress-bg);
  overflow: hidden;
}
.stat-bar-fill {
  height: 100%;
  border-radius: 4px;
  transition: width 0.5s ease;
}

/* Fade in animation */
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: translateY(0); }
}
.fade-in { animation: fadeIn 0.25s ease-out; }

/* Loading spinner */
@keyframes spin { to { transform: rotate(360deg); } }
.spinner {
  width: 32px; height: 32px;
  border: 3px solid var(--border-color);
  border-top-color: #6366f1;
  border-radius: 50%;
  animation: spin 0.7s linear infinite;
}