:root{
  --bg:#f4f6fb;
  --panel:#ffffff;
  --text:#1e293b;
  --muted:#64748b;
  --accent:#2563eb;
  --accent-2:#1d4ed8;
  --border:#e2e8f0;
  --success:#166534;
  --warning:#92400e;
  --danger:#991b1b;
  --shadow:0 8px 24px rgba(15,23,42,.08);
  --radius:16px;
}
*{box-sizing:border-box}
html,body{margin:0;padding:0;font-family:Arial,Helvetica,sans-serif;background:var(--bg);color:var(--text)}
a{color:var(--accent);text-decoration:none}
a:hover{text-decoration:underline}
.container{max-width:980px;margin:0 auto;padding:32px 18px 64px}
.hero{margin-bottom:24px}
.hero h1{margin:0 0 12px;font-size:2.3rem;line-height:1.1}
.hero p{margin:0;color:var(--muted);font-size:1.08rem}
.card{background:var(--panel);border:1px solid var(--border);border-radius:var(--radius);box-shadow:var(--shadow);padding:28px;margin:18px 0}
.card h2,.card h3{margin-top:0}
.grid{display:grid;gap:18px}
.grid.two{grid-template-columns:repeat(auto-fit,minmax(280px,1fr))}
.kicker{display:inline-block;font-size:.8rem;font-weight:bold;letter-spacing:.08em;color:var(--accent-2);text-transform:uppercase;margin-bottom:10px}
.pill{display:inline-block;padding:6px 10px;border-radius:999px;background:#e8f0ff;color:var(--accent-2);font-size:.85rem;margin-right:8px;margin-bottom:8px}
.button{display:inline-block;background:var(--accent);color:white;border:none;border-radius:10px;padding:12px 16px;font-weight:bold;cursor:pointer;text-decoration:none}
.button:hover{background:var(--accent-2);text-decoration:none}
.button.secondary{background:white;color:var(--accent);border:1px solid var(--border)}
.button.good{background:#15803d}
.button.hard{background:#b45309}
.button.again{background:#b91c1c}
.actions{display:flex;gap:12px;flex-wrap:wrap;margin-top:18px}
ul.clean{margin:12px 0 0 20px;padding:0}
ul.clean li{margin:8px 0}
.meta{color:var(--muted);font-size:.95rem}
.topic-list li{margin:10px 0}
.stat{font-size:1.8rem;font-weight:bold;margin:4px 0}
.small{font-size:.92rem;color:var(--muted)}
.sep{height:1px;background:var(--border);margin:20px 0}
.code{background:#0f172a;color:#e2e8f0;border-radius:12px;padding:14px;overflow:auto;font-family:Consolas,Monaco,monospace;font-size:.95rem}
.question{font-size:1.15rem;line-height:1.5}
.answer{margin-top:16px;padding:14px;border-radius:12px;background:#f8fafc;border:1px solid var(--border)}
.hidden{display:none !important}
.nav{display:flex;gap:14px;flex-wrap:wrap;margin-bottom:20px}
.footer{margin-top:30px;color:var(--muted);font-size:.95rem}
.choice-list{display:grid;gap:10px;margin-top:14px}
.choice{padding:12px 14px;border:1px solid var(--border);background:white;border-radius:12px;cursor:pointer;text-align:left}
.choice:hover{border-color:#bfdbfe;background:#f8fbff}
.choice.correct{border-color:#86efac;background:#f0fdf4}
.choice.incorrect{border-color:#fecaca;background:#fef2f2}
.badge{display:inline-block;background:#eff6ff;color:#1d4ed8;border:1px solid #bfdbfe;padding:4px 8px;border-radius:999px;font-size:.8rem;margin-right:8px}
@media (max-width:640px){
  .hero h1{font-size:1.9rem}
  .container{padding:20px 14px 50px}
  .card{padding:20px}
}