:root {
  --primary: #0d9488;
  --primary-dark: #0f766e;
  --bg: #f1f5f9;
  --card: #fff;
  --text: #1e293b;
  --muted: #64748b;
  --border: #e2e8f0;
  --danger: #dc2626;
  --success: #16a34a;
}
* { box-sizing: border-box; margin: 0; padding: 0; }
body { font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Helvetica, Arial, sans-serif; background: var(--bg); color: var(--text); line-height: 1.5; min-height: 100vh; }
a { color: inherit; text-decoration: none; }
.container { max-width: 680px; margin: 0 auto; padding: 0 16px; }

/* Header */
.header { background: linear-gradient(135deg, #0f766e, #0d9488); color: #fff; padding: 18px 0 20px; text-align: center; }
.header h1 { font-size: 20px; font-weight: 700; margin-bottom: 2px; }
.header p { font-size: 12px; opacity: .9; }
.back { display: inline-block; font-size: 12px; opacity: .85; margin-bottom: 8px; }
.back:hover { opacity: 1; text-decoration: underline; }

/* Top nav */
.nav { background: #fff; border-bottom: 1px solid var(--border); position: sticky; top: 0; z-index: 30; }
.nav-inner { display: flex; overflow-x: auto; gap: 2px; padding: 6px 0; }
.nav a { flex-shrink: 0; padding: 8px 12px; border-radius: 8px; font-size: 13px; font-weight: 600; color: var(--muted); }
.nav a.active, .nav a:hover { background: #0f766e; color: #fff; }

/* Section */
.section { padding: 20px 0 36px; }
.section-title { font-size: 15px; font-weight: 700; margin-bottom: 10px; color: var(--text); }

/* Cards grid */
.grid { display: grid; grid-template-columns: 1fr 1fr; gap: 10px; }
.grid-3 { display: grid; grid-template-columns: 1fr 1fr 1fr; gap: 8px; }
.card { background: var(--card); border: 1px solid var(--border); border-radius: 12px; padding: 14px; transition: .15s; }
.card:hover { border-color: var(--primary); box-shadow: 0 4px 12px rgba(13,148,136,.1); }
.card h3 { font-size: 14px; font-weight: 700; margin-bottom: 3px; }
.card p { font-size: 12px; color: var(--muted); margin-bottom: 4px; }
.card .tag { font-size: 11px; color: var(--primary); font-weight: 600; }
.card .tag-danger { color: var(--danger); }

/* Feature row (4 main tabs style) */
.feature-list { display: flex; flex-direction: column; gap: 8px; }
.feature {
  display: flex; align-items: center; gap: 12px;
  background: var(--card); border: 1px solid var(--border); border-radius: 12px;
  padding: 14px 16px; transition: .15s;
}
.feature:hover { border-color: var(--primary); }
.feature-icon { font-size: 24px; flex-shrink: 0; width: 40px; text-align: center; }
.feature-body { flex: 1; min-width: 0; }
.feature-body h3 { font-size: 14px; font-weight: 700; margin-bottom: 2px; }
.feature-body p { font-size: 12px; color: var(--muted); }
.feature-arrow { color: var(--muted); font-size: 18px; }

/* Alert */
.alert { background: #fef2f2; border: 1px solid #fecaca; border-radius: 12px; padding: 14px; margin-bottom: 16px; }
.alert-title { font-weight: 700; color: var(--danger); font-size: 13px; margin-bottom: 4px; }
.alert p { font-size: 12px; color: #7f1d1d; margin: 0; line-height: 1.5; }

/* Buttons */
.btn { display: inline-flex; align-items: center; justify-content: center; gap: 6px; padding: 11px 18px; border-radius: 10px; font-size: 14px; font-weight: 600; border: none; cursor: pointer; transition: .15s; }
.btn-primary { background: var(--primary); color: #fff; width: 100%; }
.btn-primary:hover { background: var(--primary-dark); }
.btn-outline { background: #fff; border: 1px solid var(--border); color: var(--text); }
.btn-outline:hover { border-color: var(--primary); color: var(--primary); }
.btn-danger { background: var(--danger); color: #fff; }
.btn-sm { padding: 8px 12px; font-size: 13px; }

/* Exam */
.exam-card { background: var(--card); border: 1px solid var(--border); border-radius: 14px; padding: 18px; }
.exam-top { display: flex; justify-content: space-between; align-items: center; margin-bottom: 14px; font-size: 13px; }
.timer { font-size: 18px; font-weight: 800; color: var(--danger); font-variant-numeric: tabular-nums; }
.q-text { font-size: 15px; font-weight: 600; margin-bottom: 14px; line-height: 1.45; }
.options { display: flex; flex-direction: column; gap: 8px; }
.opt { display: flex; gap: 10px; padding: 11px 12px; border: 1.5px solid var(--border); border-radius: 10px; cursor: pointer; font-size: 13px; transition: .12s; background: #fff; }
.opt:hover { border-color: var(--primary); background: #f0fdfa; }
.opt.selected { border-color: var(--primary); background: #ccfbf1; }
.opt.correct { border-color: var(--success); background: #dcfce7; }
.opt.wrong { border-color: var(--danger); background: #fee2e2; }
.opt-key { width: 22px; height: 22px; border-radius: 6px; background: #f1f5f9; display: flex; align-items: center; justify-content: center; font-weight: 700; font-size: 11px; flex-shrink: 0; }
.opt.selected .opt-key { background: var(--primary); color: #fff; }
.critical { display: inline-block; background: #fef2f2; color: var(--danger); font-size: 10px; font-weight: 700; padding: 2px 7px; border-radius: 4px; margin-left: 6px; }
.exam-actions { display: flex; gap: 8px; margin-top: 16px; flex-wrap: wrap; }
.exam-actions .btn { flex: 1; min-width: 90px; }

/* Chapter list */
.chapter-item {
  display: flex; align-items: center; justify-content: space-between;
  background: var(--card); border: 1px solid var(--border); border-radius: 10px;
  padding: 12px 14px; margin-bottom: 8px;
}
.chapter-item:hover { border-color: var(--primary); }
.chapter-info h3 { font-size: 13px; font-weight: 700; }
.chapter-info p { font-size: 11px; color: var(--muted); }

/* Result */
.result { text-align: center; padding: 24px 14px; }
.result-score { font-size: 40px; font-weight: 900; margin: 6px 0; }
.pass { color: var(--success); }
.fail { color: var(--danger); }

/* FAQ */
.faq-item { background: var(--card); border: 1px solid var(--border); border-radius: 10px; padding: 12px 14px; margin-bottom: 8px; }
.faq-item h4 { font-size: 13px; font-weight: 700; margin-bottom: 4px; }
.faq-item p { font-size: 12px; color: var(--muted); }

/* Footer */
.footer { text-align: center; padding: 20px 16px; font-size: 12px; color: var(--muted); }
.footer a { color: var(--primary); }

@media (max-width: 400px) {
  .grid, .grid-3 { grid-template-columns: 1fr; }
}