* { margin: 0; padding: 0; box-sizing: border-box; }
:root {
  --primary: #4F46E5;
  --primary-light: #6366F1;
  --primary-dark: #3730A3;
  --success: #10B981;
  --danger: #EF4444;
  --warning: #F59E0B;
  --bg: #F0F2F5;
  --card: #FFFFFF;
  --text: #1F2937;
  --text-secondary: #6B7280;
  --border: #E5E7EB;
  --radius: 12px;
  --shadow: 0 1px 3px rgba(0,0,0,.08), 0 1px 2px rgba(0,0,0,.06);
  --shadow-lg: 0 4px 6px rgba(0,0,0,.07), 0 10px 15px rgba(0,0,0,.1);
}
html { font-size: 16px; }
body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Noto Sans SC", sans-serif;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  line-height: 1.5;
}
.container { max-width: 800px; margin: 0 auto; padding: 16px; }
.card {
  background: var(--card);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 24px;
  margin-bottom: 16px;
}
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 12px 24px;
  border: none;
  border-radius: 8px;
  font-size: 16px;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s;
  text-decoration: none;
}
.btn:active { transform: scale(0.97); }
.btn-primary { background: var(--primary); color: white; }
.btn-primary:hover { background: var(--primary-light); }
.btn-success { background: var(--success); color: white; }
.btn-danger { background: var(--danger); color: white; }
.btn-warning { background: var(--warning); color: white; }
.btn-outline {
  background: transparent;
  border: 2px solid var(--primary);
  color: var(--primary);
}
.btn-outline:hover { background: var(--primary); color: white; }
.btn-sm { padding: 8px 16px; font-size: 14px; }
.btn-lg { padding: 16px 32px; font-size: 18px; }
.btn-block { width: 100%; }
.btn:disabled { opacity: 0.5; cursor: not-allowed; }

.form-group { margin-bottom: 16px; }
.form-group label {
  display: block;
  font-weight: 600;
  margin-bottom: 6px;
  color: var(--text);
}
.form-input {
  width: 100%;
  padding: 12px 16px;
  border: 2px solid var(--border);
  border-radius: 8px;
  font-size: 16px;
  outline: none;
  transition: border-color 0.2s;
}
.form-input:focus { border-color: var(--primary); }

.badge {
  display: inline-block;
  padding: 4px 12px;
  border-radius: 20px;
  font-size: 13px;
  font-weight: 600;
}
.badge-primary { background: #EEF2FF; color: var(--primary); }
.badge-success { background: #D1FAE5; color: #065F46; }
.badge-danger { background: #FEE2E2; color: #991B1B; }
.badge-warning { background: #FEF3C7; color: #92400E; }

.text-center { text-align: center; }
.text-success { color: var(--success); }
.text-danger { color: var(--danger); }
.text-primary { color: var(--primary); }
.text-secondary { color: var(--text-secondary); }
.mt-4 { margin-top: 16px; }
.mt-8 { margin-top: 32px; }
.mb-4 { margin-bottom: 16px; }
.mb-8 { margin-bottom: 32px; }

.logo {
  font-size: 28px;
  font-weight: 800;
  color: var(--primary);
  text-align: center;
  margin: 32px 0 8px;
}
.subtitle { color: var(--text-secondary); text-align: center; margin-bottom: 24px; }

/* Landing Page */
.landing-card { text-align: center; padding: 48px 24px; }
.landing-card .icon { font-size: 64px; margin-bottom: 16px; }
.qr-container {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 16px;
  margin: 24px 0;
}
.qr-container img { max-width: 280px; border-radius: 12px; box-shadow: var(--shadow-lg); }

/* Options list */
.options-list { list-style: none; }
.options-list li {
  padding: 14px 18px;
  margin-bottom: 10px;
  border: 2px solid var(--border);
  border-radius: 10px;
  cursor: pointer;
  transition: all 0.2s;
  font-size: 16px;
  display: flex;
  align-items: center;
  gap: 12px;
}
.options-list li:hover { border-color: var(--primary-light); background: #EEF2FF; }
.options-list li.selected { border-color: var(--primary); background: #EEF2FF; }
.options-list li.correct { border-color: var(--success); background: #D1FAE5; }
.options-list li.wrong { border-color: var(--danger); background: #FEE2E2; }
.options-list li.disabled { cursor: default; opacity: 0.7; }
.options-list li .letter {
  width: 30px; height: 30px;
  border-radius: 50%;
  background: var(--bg);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 14px;
  flex-shrink: 0;
}
.options-list li.selected .letter { background: var(--primary); color: white; }
.options-list li.correct .letter { background: var(--success); color: white; }
.options-list li.wrong .letter { background: var(--danger); color: white; }

/* Timer */
.timer {
  text-align: center;
  margin: 16px 0;
  font-size: 48px;
  font-weight: 800;
  color: var(--primary);
}
.timer.warning { color: var(--warning); }
.timer.danger { color: var(--danger); animation: pulse 0.5s infinite; }
@keyframes pulse {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.5; }
}

/* Progress bar */
.progress-bar {
  height: 6px;
  background: var(--border);
  border-radius: 3px;
  overflow: hidden;
  margin: 16px 0;
}
.progress-bar .fill {
  height: 100%;
  background: var(--primary);
  border-radius: 3px;
  transition: width 0.3s;
}
.progress-bar .fill.warning { background: var(--warning); }
.progress-bar .fill.danger { background: var(--danger); }

/* Admin stats bar */
.stats-bar {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
  margin: 16px 0;
}
.stat-item {
  flex: 1;
  min-width: 100px;
  text-align: center;
  padding: 12px;
  background: var(--bg);
  border-radius: 8px;
}
.stat-item .num { font-size: 28px; font-weight: 800; color: var(--primary); }
.stat-item .label { font-size: 13px; color: var(--text-secondary); }

/* Leaderboard */
.leaderboard { width: 100%; border-collapse: collapse; }
.leaderboard th {
  background: var(--bg);
  font-size: 13px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  padding: 12px 8px;
  text-align: left;
  color: var(--text-secondary);
}
.leaderboard td { padding: 12px 8px; border-bottom: 1px solid var(--border); }
.leaderboard .rank {
  font-weight: 800;
  font-size: 18px;
  color: var(--primary);
  width: 40px;
}
.leaderboard .rank-1 { color: #F59E0B; }
.leaderboard .rank-2 { color: #9CA3AF; }
.leaderboard .rank-3 { color: #D97706; }

/* Question type badge */
.q-type {
  display: inline-block;
  padding: 2px 10px;
  border-radius: 12px;
  font-size: 12px;
  font-weight: 600;
}
.q-type.single { background: #DBEAFE; color: #1E40AF; }
.q-type.truefalse { background: #D1FAE5; color: #065F46; }
.q-type.multiple { background: #FEF3C7; color: #92400E; }

/* Admin question list */
.q-list-item {
  padding: 16px;
  border: 1px solid var(--border);
  border-radius: 8px;
  margin-bottom: 8px;
  cursor: pointer;
  transition: all 0.2s;
}
.q-list-item:hover { border-color: var(--primary-light); }
.q-list-item.active { border-color: var(--primary); background: #EEF2FF; }
.q-list-item.completed { border-color: var(--success); }

/* Responsive */
@media (max-width: 640px) {
  .container { padding: 12px; }
  .card { padding: 16px; }
  .stats-bar { flex-direction: column; }
  .stat-item { min-width: auto; }
  .timer { font-size: 36px; }
}

/* Transition */
.fade-in { animation: fadeIn 0.3s ease; }
@keyframes fadeIn { from { opacity: 0; transform: translateY(10px); } to { opacity: 1; transform: translateY(0); } }

/* Checkbox for multiple choice */
.checkbox-box {
  width: 22px; height: 22px;
  border: 2px solid var(--border);
  border-radius: 4px;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  transition: all 0.2s;
}
.options-list li.selected .checkbox-box { background: var(--primary); border-color: var(--primary); color: white; }
.options-list li.correct .checkbox-box { background: var(--success); border-color: var(--success); color: white; }
.options-list li.wrong .checkbox-box { background: var(--danger); border-color: var(--danger); color: white; }

/* Hidden utility */
.hidden { display: none !important; }