:root {
  --bg: #f2f5fb;
  --card: #ffffff;
  --text: #1e293b;
  --muted: #64748b;
  --primary: #2563eb;
  --primary-dark: #1d4ed8;
  --good: #16a34a;
  --bad: #dc2626;
  --warn: #d97706;
  --border: #e2e8f0;
  --radius: 14px;
  --shadow: 0 1px 3px rgba(15, 23, 42, .08), 0 8px 24px rgba(15, 23, 42, .06);
}

* { box-sizing: border-box; margin: 0; padding: 0; }
body {
  font-family: system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.55;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}
a { color: var(--primary); text-decoration: none; }
a:hover { text-decoration: underline; }
.container { width: 100%; max-width: 1024px; margin: 0 auto; padding: 0 16px; }
main.container { flex: 1; padding-top: 24px; padding-bottom: 48px; }

/* topbar */
.topbar {
  background: #0f172a;
  color: #fff;
  position: sticky; top: 0; z-index: 50;
}
.btn-danger { color: #b91c1c; border-color: #fecaca; background: #fff; }
.btn-danger:hover { background: #fef2f2; }
.learn-nav { display: flex; gap: 10px; align-items: center; justify-content: space-between; margin-top: 18px; flex-wrap: wrap; }
.brand { color: #fff; font-weight: 800; font-size: 1.2rem; }
.brand:hover { text-decoration: none; }
.nav { display: flex; align-items: center; gap: 12px; color: #cbd5e1; }
.nav a { color: #e2e8f0; }
.user-chip { font-size: .9rem; }
.inline-form { display: inline; }

/* buttons */
.btn {
  display: inline-block;
  padding: 8px 16px;
  border-radius: 10px;
  border: 1px solid transparent;
  font-size: .95rem;
  font-weight: 600;
  cursor: pointer;
  transition: .15s;
  text-decoration: none !important;
  background: transparent;
  color: var(--text);
}
.btn-sm { padding: 5px 12px; font-size: .85rem; }
.btn-block { width: 100%; }
.btn-primary { background: var(--primary); color: #fff; }
.btn-primary:hover { background: var(--primary-dark); }
.btn-outline { border-color: var(--primary); color: var(--primary); background: #fff; }
.btn-outline:hover { background: #eff6ff; }
.btn-ghost { color: var(--muted); }
.btn-ghost:hover { background: #eef2f7; color: var(--text); }
.btn-warn { background: #fef3c7; color: #92400e; border-color: #fcd34d; }
.btn-success { background: var(--good); color: #fff; }
.btn-success:hover { background: #15803d; }
.topbar .btn-ghost { color: #cbd5e1; }
.topbar .btn-ghost:hover { background: rgba(255,255,255,.1); color: #fff; }
.topbar .btn-primary { background: var(--primary); }

/* cards */
.card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 20px;
  margin-bottom: 20px;
}
.card h2 { font-size: 1.15rem; margin-bottom: 12px; }
.muted { color: var(--muted); }

/* hero */
.hero {
  text-align: center;
  padding: 48px 16px 32px;
  background: linear-gradient(135deg, #1e3a8a, #2563eb 60%, #3b82f6);
  color: #fff;
  border-radius: 20px;
  margin-bottom: 28px;
}
.hero h1 { font-size: 2rem; margin-bottom: 10px; }
.hero p { max-width: 640px; margin: 0 auto; opacity: .92; }

/* course grid */
.course-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(300px, 1fr)); gap: 18px; }
.course-card { display: flex; flex-direction: column; gap: 10px; margin-bottom: 0; }
.course-head { display: flex; align-items: center; gap: 12px; }
.course-icon { font-size: 1.6rem; }
.course-icon.big { font-size: 2.6rem; }
.course-head h2 { font-size: 1.1rem; margin: 0; }
.course-desc { color: var(--muted); font-size: .92rem; flex: 1; }
.course-meta { font-size: .85rem; color: var(--muted); }
.course-actions { display: flex; gap: 8px; flex-wrap: wrap; margin-top: 4px; }
.course-actions.center { justify-content: center; }

/* progress */
.progress-block { margin: 8px 0 14px; }
.progress-label { font-size: .85rem; color: var(--muted); margin-bottom: 6px; display: flex; gap: 10px; align-items: baseline; flex-wrap: wrap; }
.progress-bar { height: 8px; background: #e2e8f0; border-radius: 99px; overflow: hidden; }
.progress-fill { height: 100%; background: linear-gradient(90deg, var(--primary), #38bdf8); border-radius: 99px; transition: width .3s; }

/* stats */
.stats-row { display: grid; grid-template-columns: repeat(auto-fit, minmax(110px, 1fr)); gap: 12px; margin-bottom: 12px; }
.stat { background: #f8fafc; border: 1px solid var(--border); border-radius: 12px; padding: 14px; text-align: center; }
.stat b { display: block; font-size: 1.5rem; color: var(--primary); }
.stat.good b { color: var(--good); }
.stat.bad b { color: var(--bad); }
.stat span { font-size: .8rem; color: var(--muted); }

/* auth */
.auth-wrap { display: flex; justify-content: center; padding-top: 40px; }
.auth-card { width: 100%; max-width: 400px; }
.auth-card h1 { margin-bottom: 16px; font-size: 1.4rem; }
.form label { display: block; margin-bottom: 14px; font-size: .9rem; font-weight: 600; }
.form input {
  display: block; width: 100%; margin-top: 6px;
  padding: 10px 12px; border: 1px solid var(--border); border-radius: 10px;
  font-size: 1rem;
}
.form input:focus { outline: 2px solid var(--primary); border-color: transparent; }
.auth-alt { margin-top: 14px; text-align: center; font-size: .9rem; }

/* alerts */
.alert { padding: 12px 14px; border-radius: 10px; margin-bottom: 14px; font-size: .92rem; }
.alert-error { background: #fef2f2; color: #991b1b; border: 1px solid #fecaca; }
.alert-warn { background: #fffbeb; color: #92400e; border: 1px solid #fde68a; }

/* question */
.q-num { font-size: .8rem; color: var(--muted); font-weight: 700; margin-bottom: 8px; }
.q-content { font-size: 1.12rem; margin-bottom: 16px; white-space: pre-line; }
.q-img { display: block; max-width: 100%; max-height: 300px; margin: 0 auto 14px; border-radius: 10px; border: 1px solid var(--border, #e2e8f0); }
.q-img-sm { max-height: 140px; margin: 0 0 8px; }
.review-q .q-img-sm { display: block; margin-bottom: 8px; }
.opts { display: flex; flex-direction: column; gap: 10px; }
.opt-btn {
  display: flex; gap: 12px; align-items: flex-start; text-align: left;
  padding: 13px 14px; border: 1.5px solid var(--border); border-radius: 12px;
  background: #fff; cursor: pointer; font-size: .98rem; transition: .12s;
  font-family: inherit; color: var(--text); width: 100%;
}
.opt-btn:hover { border-color: var(--primary); background: #eff6ff; }
.opt-letter {
  flex-shrink: 0; width: 26px; height: 26px; border-radius: 8px;
  background: #e2e8f0; color: #475569; font-weight: 800; font-size: .85rem;
  display: flex; align-items: center; justify-content: center;
}
.opt-btn.opt-selected { border-color: var(--primary); background: #eff6ff; }
.opt-btn.opt-selected .opt-letter { background: var(--primary); color: #fff; }
.opt-btn.opt-correct { border-color: var(--good); background: #f0fdf4; }
.opt-btn.opt-correct .opt-letter { background: var(--good); color: #fff; }
.opt-btn.opt-wrong { border-color: var(--bad); background: #fef2f2; }
.opt-btn.opt-wrong .opt-letter { background: var(--bad); color: #fff; }
.opt-btn.opt-show-right { border-color: var(--good); background: #ecfdf5; }
.opt-btn.opt-show-right .opt-letter { background: var(--good); color: #fff; }
.explain { margin-top: 14px; padding: 12px 14px; border-radius: 10px; font-size: .95rem; font-weight: 600; }
.explain.ok { background: #f0fdf4; color: #166534; border: 1px solid #bbf7d0; }
.explain.no { background: #fef2f2; color: #991b1b; border: 1px solid #fecaca; }
.learn-nav { display: flex; justify-content: space-between; margin-top: 18px; gap: 10px; }
.learn-nav .btn-danger { margin-left: auto; }
.topic-tag { background: #ede9fe; color: #6d28d9; padding: 2px 10px; border-radius: 99px; font-size: .78rem; }
.empty-state { text-align: center; padding: 48px 20px; }
.empty-state p { margin-bottom: 16px; font-size: 1.05rem; }

/* exam */
.exam-head { display: flex; justify-content: space-between; align-items: flex-start; gap: 16px; margin-bottom: 14px; flex-wrap: wrap; }
.exam-head h1 { font-size: 1.2rem; }
.exam-timer {
  background: #0f172a; color: #fff; padding: 10px 18px; border-radius: 12px;
  font-weight: 800; font-size: 1.25rem; font-variant-numeric: tabular-nums;
}
.exam-timer.urgent { background: var(--bad); animation: pulse 1s infinite; }
@keyframes pulse { 50% { opacity: .7; } }
.exam-layout { display: grid; grid-template-columns: 1fr 260px; gap: 18px; align-items: start; }
@media (max-width: 760px) { .exam-layout { grid-template-columns: 1fr; } }
.exam-side h3 { font-size: .95rem; margin-bottom: 10px; }
.qgrid { display: grid; grid-template-columns: repeat(auto-fill, minmax(38px, 1fr)); gap: 6px; margin-bottom: 12px; }
.qdot {
  height: 38px; border-radius: 9px; background: #f1f5f9; border: 1.5px solid var(--border);
  display: flex; align-items: center; justify-content: center; font-size: .82rem; font-weight: 700; color: var(--muted);
}
.qdot:hover { text-decoration: none; border-color: var(--primary); }
.qdot.answered { background: #dcfce7; border-color: #86efac; color: #166534; }
.qdot.current { border-color: var(--primary); background: var(--primary); color: #fff; }
.legend { display: flex; flex-direction: column; gap: 4px; font-size: .8rem; color: var(--muted); margin-bottom: 14px; }
.legend span { display: flex; align-items: center; gap: 6px; }
.legend .dot { width: 12px; height: 12px; border-radius: 4px; display: inline-block; background: #f1f5f9; border: 1px solid var(--border); }
.legend .dot.answered { background: #86efac; border-color: #86efac; }
.legend .dot.current { background: var(--primary); border-color: var(--primary); }

/* result */
.result-hero { text-align: center; padding: 36px 20px; }
.result-hero h1 { font-size: 1.8rem; margin-bottom: 8px; }
.result-score { font-size: 3rem; font-weight: 800; }
.result-pass { border-top: 6px solid var(--good); }
.result-pass .result-score { color: var(--good); }
.result-fail { border-top: 6px solid var(--bad); }
.result-fail .result-score { color: var(--bad); }
.review-item { border-top: 1px solid var(--border); padding: 16px 0; }
.review-item:first-of-type { border-top: none; }
.review-mark { display: flex; gap: 8px; margin-bottom: 8px; }
.review-q { font-weight: 600; margin-bottom: 10px; }
.review-opts { display: flex; flex-direction: column; gap: 6px; }
.review-opt { display: flex; gap: 10px; padding: 8px 10px; border-radius: 8px; background: #f8fafc; font-size: .92rem; align-items: baseline; }
.review-opt .opt-letter { width: 22px; height: 22px; font-size: .75rem; }
.review-right { background: #f0fdf4; outline: 1px solid #bbf7d0; }
.review-picked { background: #fef2f2; outline: 1px solid #fecaca; }

/* badges & table */
.badge { display: inline-block; padding: 2px 10px; border-radius: 99px; font-size: .78rem; font-weight: 700; background: #e2e8f0; color: #475569; }
.badge-good { background: #dcfce7; color: #166534; }
.badge-bad { background: #fee2e2; color: #991b1b; }
.badge-warn { background: #fef3c7; color: #92400e; }
.table { width: 100%; border-collapse: collapse; font-size: .92rem; }
.table th, .table td { text-align: left; padding: 9px 10px; border-bottom: 1px solid var(--border); }
.table .num { text-align: right; }
.table th { color: var(--muted); font-size: .8rem; text-transform: uppercase; letter-spacing: .03em; }

/* progress page */
.page-title { margin-bottom: 20px; }
.course-row { display: flex; justify-content: space-between; align-items: center; gap: 14px; padding: 14px 0; border-bottom: 1px solid var(--border); flex-wrap: wrap; }
.course-row:last-child { border-bottom: none; }
.course-row-main { display: flex; gap: 12px; align-items: flex-start; flex: 1; min-width: 240px; }
.course-title { font-weight: 700; }
.course-row .progress-bar { max-width: 420px; }
.course-row-actions { display: flex; gap: 6px; }

.footer { padding: 20px; color: var(--muted); font-size: .85rem; border-top: 1px solid var(--border); background: #fff; }