:root{--bg:#fff;--fg:#1a1a1a;--muted:#6b7280;--border:#e5e7eb;--accent:#2563eb;--accent-hover:#1d4ed8;--card:#f9fafb;--max-width:1100px}*{box-sizing:border-box}body,html{margin:0;padding:0;background:var(--bg);color:var(--fg);font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Helvetica Neue,Arial,sans-serif;font-size:16px;line-height:1.5;-webkit-font-smoothing:antialiased}a{color:var(--accent);text-decoration:none}a:hover{color:var(--accent-hover);text-decoration:underline}.container{max-width:var(--max-width);margin:0 auto;padding:16px}.site-header{border-bottom:1px solid var(--border);background:#fff}.site-header .container{display:flex;align-items:center;justify-content:space-between;gap:16px}.brand{font-size:1.25rem;font-weight:700;color:var(--fg)}.brand:hover{text-decoration:none}h1{font-size:1.75rem;margin:16px 0 8px}h2{font-size:1.25rem;margin:24px 0 8px}.lead{color:var(--muted);margin:0 0 24px}.breadcrumbs{font-size:.875rem;margin:12px 0 16px}.breadcrumbs,.breadcrumbs a{color:var(--muted)}.breadcrumbs a:hover{color:var(--accent)}.breadcrumbs span+span:before{content:" › ";margin:0 4px}.grid{display:grid;grid-gap:12px;gap:12px;grid-template-columns:repeat(2,1fr)}@media (min-width:600px){.grid{grid-template-columns:repeat(3,1fr)}}@media (min-width:900px){.grid-subjects{grid-template-columns:repeat(4,1fr)}}.card{display:block;padding:16px;border:1px solid var(--border);border-radius:10px;background:var(--card);color:var(--fg);transition:border-color .15s,transform .15s}.card:hover{border-color:var(--accent);text-decoration:none;transform:translateY(-1px)}.card .icon{font-size:1.75rem;display:block;margin-bottom:6px}.card .title{font-weight:600}.card .meta{font-size:.8125rem;color:var(--muted);margin-top:4px}.grade-pills{display:flex;flex-wrap:wrap;gap:8px;margin:16px 0 24px}.grade-pills a{display:inline-block;padding:6px 12px;border:1px solid var(--border);border-radius:999px;background:#fff;color:var(--fg);font-size:.875rem}.grade-pills a:hover{border-color:var(--accent);text-decoration:none}.list-plain{list-style:none;padding:0;margin:0}.list-plain li{padding:12px 0;border-bottom:1px solid var(--border)}.list-plain li:last-child{border-bottom:none}.exercise-grid{display:grid;grid-gap:8px;gap:8px;grid-template-columns:repeat(auto-fill,minmax(80px,1fr));margin-top:8px}.exercise-grid a{display:block;text-align:center;padding:10px 6px;border:1px solid var(--border);border-radius:8px;background:#fff;color:var(--fg);font-size:.875rem}.exercise-grid a:hover{border-color:var(--accent);text-decoration:none}.solution{margin-top:16px}.solution img{max-width:100%;height:auto;display:block;margin:12px 0;border:1px solid var(--border);border-radius:8px}.solution pre{white-space:pre-wrap;word-wrap:break-word;background:var(--card);padding:12px;border-radius:8px}footer{margin-top:48px;padding:24px 0;border-top:1px solid var(--border);color:var(--muted);font-size:.875rem;text-align:center}