:root {
  --bg: #0d1117;
  --bg-elev: #161b22;
  --bg-card: #1c2230;
  --border: #2a3140;
  --border-strong: #3a4253;
  --text: #e6edf3;
  --text-dim: #8b949e;
  --text-muted: #6b7280;
  --accent: #d97706;
  --accent-hover: #b45309;
  --accent-dim: #422006;
  --ok: #10b981;
  --ok-bg: #064e3b;
  --err: #ef4444;
  --err-bg: #4c1d1d;
  --info: #3b82f6;
  --warn: #f59e0b;
  --radius: 10px;
  --radius-lg: 16px;
  --shadow: 0 4px 20px rgba(0,0,0,.35);
  --mono: "JetBrains Mono", ui-monospace, SFMono-Regular, Menlo, monospace;
}

* { box-sizing: border-box; }
html, body { height: 100%; }
body {
  margin: 0;
  font-family: "Inter", system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  background: var(--bg);
  color: var(--text);
  -webkit-font-smoothing: antialiased;
  line-height: 1.55;
}

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

#app { min-height: 100vh; display: flex; flex-direction: column; }

.topbar {
  display: flex; align-items: center; justify-content: space-between;
  padding: 16px 28px; border-bottom: 1px solid var(--border);
  background: rgba(13,17,23,.95); backdrop-filter: blur(8px);
  position: sticky; top: 0; z-index: 10;
}
.brand { font-weight: 800; letter-spacing: -.02em; font-size: 18px; }
.brand .dot { color: var(--accent); }
.topbar .meta { font-size: 13px; color: var(--text-dim); font-family: var(--mono); }

.container { width: 100%; max-width: 980px; margin: 0 auto; padding: 32px 24px 80px; }
.container.wide { max-width: 1180px; }

h1 { font-size: 32px; letter-spacing: -.02em; margin: 0 0 8px; font-weight: 800; }
h2 { font-size: 22px; margin: 0 0 12px; font-weight: 700; }
p.lede { color: var(--text-dim); margin: 0 0 28px; font-size: 16px; }

.cards { display: grid; grid-template-columns: 1fr 1fr; gap: 20px; margin-top: 24px; }
@media (max-width: 720px) { .cards { grid-template-columns: 1fr; } }
.card {
  background: var(--bg-card); border: 1px solid var(--border);
  border-radius: var(--radius-lg); padding: 28px;
  transition: border-color .2s, transform .15s;
  display: flex; flex-direction: column;
}
.card:hover { border-color: var(--border-strong); }
.card h3 { font-size: 19px; margin: 0 0 6px; font-weight: 700; }
.card p { color: var(--text-dim); margin: 0 0 18px; font-size: 14px; flex: 1; }
.card .tag { display: inline-block; font-size: 11px; padding: 3px 8px; border-radius: 6px; font-family: var(--mono);
  background: var(--accent-dim); color: var(--accent); margin-bottom: 12px; letter-spacing: .04em; text-transform: uppercase; }
.card.alt .tag { background: #0d2942; color: #60a5fa; }

button, .btn {
  appearance: none; border: 0; padding: 11px 18px; border-radius: 8px;
  font-family: inherit; font-size: 14px; font-weight: 600; cursor: pointer;
  background: var(--accent); color: white; transition: background .15s;
}
button:hover, .btn:hover { background: var(--accent-hover); }
button:disabled { background: #444; cursor: not-allowed; color: #999; }
.btn-ghost { background: transparent; color: var(--text); border: 1px solid var(--border-strong); }
.btn-ghost:hover { background: var(--bg-elev); }
.btn-danger { background: var(--err); }
.btn-danger:hover { background: #b91c1c; }
.btn-row { display: flex; gap: 10px; flex-wrap: wrap; }

.stats { display: grid; grid-template-columns: repeat(auto-fit, minmax(140px, 1fr)); gap: 12px; margin-bottom: 28px; }
.stat { background: var(--bg-card); border: 1px solid var(--border); border-radius: var(--radius); padding: 14px 16px; }
.stat .k { font-size: 11px; color: var(--text-dim); text-transform: uppercase; letter-spacing: .06em; }
.stat .v { font-size: 22px; font-weight: 700; font-family: var(--mono); margin-top: 4px; }
.stat .v.ok { color: var(--ok); }
.stat .v.err { color: var(--err); }

/* Exam runner */
.runner { display: grid; grid-template-columns: 1fr 280px; gap: 24px; align-items: start; }
@media (max-width: 980px) { .runner { grid-template-columns: 1fr; } }

.qbox { background: var(--bg-card); border: 1px solid var(--border); border-radius: var(--radius-lg); padding: 28px; }
.qhead { display: flex; justify-content: space-between; align-items: center; margin-bottom: 14px; }
.qmeta { font-family: var(--mono); font-size: 12px; color: var(--text-dim); }
.qmeta .src { background: var(--bg-elev); padding: 2px 8px; border-radius: 4px; }
.qnum { font-size: 13px; color: var(--text-dim); font-family: var(--mono); }
.qstem { font-size: 16px; line-height: 1.65; margin: 0 0 22px; white-space: pre-wrap; }
.qstem code, .qmeta code {
  font-family: var(--mono); font-size: .92em; background: var(--bg-elev);
  padding: 1px 6px; border-radius: 4px; color: #f3b066;
}

.options { display: flex; flex-direction: column; gap: 10px; }
.opt {
  display: flex; gap: 12px; padding: 14px 16px; border: 1px solid var(--border);
  border-radius: var(--radius); cursor: pointer; transition: border-color .15s, background .15s;
  background: var(--bg-elev);
}
.opt:hover { border-color: var(--border-strong); }
.opt input { margin-top: 4px; accent-color: var(--accent); }
.opt .letter { font-family: var(--mono); font-weight: 600; color: var(--accent); min-width: 22px; }
.opt .text { flex: 1; font-size: 14.5px; line-height: 1.55; }
.opt.selected { border-color: var(--accent); background: rgba(217,119,6,.08); }
.opt.correct { border-color: var(--ok); background: rgba(16,185,129,.10); }
.opt.wrong { border-color: var(--err); background: rgba(239,68,68,.10); }
.opt.expected { border-color: var(--ok); background: rgba(16,185,129,.06); }

.qactions { display: flex; justify-content: space-between; align-items: center; margin-top: 24px; gap: 12px; }

/* Sidebar */
.sidebar { background: var(--bg-card); border: 1px solid var(--border); border-radius: var(--radius-lg); padding: 20px;
  position: sticky; top: 80px; }
.sidebar h4 { margin: 0 0 12px; font-size: 13px; color: var(--text-dim); text-transform: uppercase; letter-spacing: .06em; }
.timer { font-family: var(--mono); font-size: 38px; font-weight: 700; text-align: center; letter-spacing: .02em; padding: 8px 0 12px; }
.timer.warn { color: var(--warn); }
.timer.danger { color: var(--err); animation: pulse 1.5s ease-in-out infinite; }
@keyframes pulse { 0%, 100% { opacity: 1; } 50% { opacity: .55; } }
.timer-actions { display: flex; gap: 8px; margin-bottom: 16px; }
.timer-actions button { flex: 1; font-size: 12px; padding: 8px; }

.qgrid { display: grid; grid-template-columns: repeat(6, 1fr); gap: 5px; margin-top: 12px; }
.qgrid .cell {
  font-family: var(--mono); font-size: 11px; padding: 7px 0; text-align: center;
  border: 1px solid var(--border); border-radius: 5px; cursor: pointer; background: var(--bg-elev);
  transition: all .12s;
}
.qgrid .cell:hover { border-color: var(--border-strong); }
.qgrid .cell.answered { background: var(--accent-dim); border-color: var(--accent); color: var(--accent); }
.qgrid .cell.current { background: var(--accent); border-color: var(--accent); color: white; }
.qgrid .cell.correct { background: var(--ok-bg); border-color: var(--ok); color: var(--ok); }
.qgrid .cell.wrong { background: var(--err-bg); border-color: var(--err); color: var(--err); }

.result-banner {
  padding: 24px 28px; border-radius: var(--radius-lg); margin-bottom: 28px;
  background: linear-gradient(135deg, #1f2937, #111827); border: 1px solid var(--border-strong);
}
.result-banner.pass { border-color: var(--ok); }
.result-banner.fail { border-color: var(--err); }
.result-banner h2 { margin: 0 0 8px; }
.result-banner .score { font-family: var(--mono); font-size: 46px; font-weight: 700; margin: 8px 0; }
.score.pass { color: var(--ok); }
.score.fail { color: var(--err); }

.expl {
  margin-top: 18px; padding: 14px 16px; background: var(--bg-elev);
  border-left: 3px solid var(--info); border-radius: 6px; font-size: 14px;
  color: var(--text-dim);
}
.expl b { color: var(--text); }

.loader { display: flex; justify-content: center; align-items: center; padding: 60px; color: var(--text-dim); }
.spinner { width: 28px; height: 28px; border: 3px solid var(--border-strong); border-top-color: var(--accent);
  border-radius: 50%; animation: spin .9s linear infinite; margin-right: 12px; }
@keyframes spin { to { transform: rotate(360deg); } }

.empty { text-align: center; padding: 60px 20px; color: var(--text-dim); }

footer { text-align: center; padding: 24px; color: var(--text-muted); font-size: 12px; border-top: 1px solid var(--border); margin-top: auto; }
footer code { font-family: var(--mono); color: var(--text-dim); }

.error-banner { background: var(--err-bg); border: 1px solid var(--err); padding: 14px 18px; border-radius: var(--radius); margin-bottom: 20px; color: #fecaca; }

.toggle { display: inline-flex; align-items: center; gap: 8px; font-size: 13px; color: var(--text-dim); cursor: pointer; user-select: none; }
.toggle input { accent-color: var(--accent); }

/* Downloads section */
.downloads { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; margin-top: 12px; }
@media (max-width: 720px) { .downloads { grid-template-columns: 1fr; } }
.download-card {
  display: flex; align-items: center; gap: 16px; padding: 16px 18px;
  background: var(--bg-card); border: 1px solid var(--border); border-radius: var(--radius);
  text-decoration: none; color: var(--text); transition: border-color .15s, transform .12s;
}
.download-card:hover { border-color: var(--accent); text-decoration: none; transform: translateY(-1px); }
.dl-icon {
  display: flex; align-items: center; justify-content: center;
  width: 44px; height: 44px; border-radius: 8px;
  background: var(--accent-dim); color: var(--accent);
  font-family: var(--mono); font-size: 11px; font-weight: 700; letter-spacing: .04em; flex-shrink: 0;
}
.dl-icon.answers { background: rgba(16,185,129,.12); color: var(--ok); }
.dl-meta { flex: 1; min-width: 0; }
.dl-title { font-weight: 600; font-size: 15px; }
.dl-sub { color: var(--text-dim); font-size: 12px; margin-top: 2px; font-family: var(--mono); }
.dl-arrow { color: var(--text-dim); font-size: 20px; transition: transform .15s; }
.download-card:hover .dl-arrow { color: var(--accent); transform: translateY(2px); }

/* Source filter */
.filter-bar { display: flex; gap: 8px; margin-bottom: 18px; flex-wrap: wrap; align-items: center; font-size: 13px; }
.filter-bar label { color: var(--text-dim); }
.filter-bar select { background: var(--bg-elev); color: var(--text); border: 1px solid var(--border); padding: 6px 10px; border-radius: 6px; font-family: inherit; }