:root{--bg:#f3f6fb;--panel:#ffffff;--text:#1f2937;--muted:#64748b;--line:#e5e7eb;--link:#0f62fe;--nav:#0f172a;--nav2:#1e293b;--blue:#1d4ed8;--blue-soft:#eff6ff}
*{box-sizing:border-box}
body{margin:0;font-family:Arial,Helvetica,sans-serif;background:linear-gradient(180deg,#eef4ff 0,#f7f9fc 200px,#f7f9fc 100%);color:var(--text)}
.layout{display:grid;grid-template-columns:320px minmax(0,1fr);min-height:100vh}
.sidebar{background:var(--nav);color:#e2e8f0;padding:20px;position:sticky;top:0;height:100vh;overflow:auto}
.brand a{color:#fff;text-decoration:none;font-weight:700;font-size:22px}
.nav-group{margin-top:24px}
.nav-heading{font-size:12px;text-transform:uppercase;letter-spacing:.08em;color:#94a3b8;margin-bottom:8px}
.sidebar ul{list-style:none;padding:0;margin:0}
.sidebar li{margin:0 0 8px 0}
.sidebar a{color:#cbd5e1;text-decoration:none;display:block;padding:9px 11px;border-radius:10px;line-height:1.3}
.sidebar a:hover{background:var(--nav2);color:#fff}
.sidebar a.active{background:#1d4ed8;color:#fff;font-weight:700}
.content{padding:32px}
.article{max-width:1100px;margin:0 auto;background:var(--panel);border:1px solid var(--line);border-radius:20px;padding:32px;box-shadow:0 10px 30px rgba(15,23,42,.07)}
.hero{margin:-6px 0 24px 0;padding:4px 0 10px 0;border-bottom:1px solid var(--line)}
.breadcrumbs{font-size:13px;color:var(--muted);margin-bottom:10px}
.breadcrumbs a{color:var(--muted);text-decoration:none}
.hero-title{font-size:2.1rem;line-height:1.15;margin:0 0 12px 0;color:#0f172a}
.hero-text{font-size:1rem;color:#334155;max-width:900px}
.chip-row{display:flex;gap:8px;flex-wrap:wrap;margin:6px 0 10px 0}
.chip{display:inline-block;background:#eef2ff;color:#1e3a8a;border:1px solid #c7d2fe;padding:6px 10px;border-radius:999px;font-size:13px;font-weight:700}
.progress-panel{margin:14px 0 8px 0;padding:14px;border:1px solid #dbeafe;background:var(--blue-soft);border-radius:14px}
.progress-label-row{display:flex;justify-content:space-between;gap:12px;font-size:14px;margin-bottom:8px}
.progress-track{width:100%;height:10px;background:#dbeafe;border-radius:999px;overflow:hidden}
.progress-fill{height:100%;background:linear-gradient(90deg,#2563eb,#60a5fa)}
.tile-section{margin:8px 0 28px 0}
.tile-section h2{margin-bottom:14px}
.tile-grid,.feature-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(220px,1fr));gap:16px}
.lesson-tile,.feature-card{display:block;text-decoration:none;color:inherit;background:#fff;border:1px solid var(--line);border-radius:16px;padding:18px;box-shadow:0 6px 18px rgba(15,23,42,.05);transition:transform .15s ease, box-shadow .15s ease, border-color .15s ease}
.lesson-tile:hover,.feature-card:hover{transform:translateY(-2px);box-shadow:0 12px 24px rgba(15,23,42,.08);border-color:#bfdbfe}
.lesson-tile.resource{background:#f8fafc}
.lesson-kicker{font-size:12px;text-transform:uppercase;letter-spacing:.08em;color:#64748b;margin-bottom:8px}
.lesson-title{font-size:18px;font-weight:700;color:#0f172a;line-height:1.25;margin-bottom:8px}
.lesson-meta{font-size:14px;color:#64748b}
.markdown-body h1,.markdown-body h2,.markdown-body h3{color:#0f172a}
.markdown-body img{max-width:100%;height:auto;border:1px solid var(--line);border-radius:12px;margin:18px 0}
.markdown-body table{width:100%;border-collapse:collapse;margin:18px 0}
.markdown-body th,.markdown-body td{border:1px solid var(--line);padding:10px;text-align:left;vertical-align:top}
.markdown-body code{background:#f1f5f9;padding:2px 5px;border-radius:4px}
.markdown-body pre code{display:block;padding:16px;overflow:auto}
.markdown-body a{color:var(--link)}
.markdown-body blockquote{margin:16px 0;padding:12px 16px;border-left:4px solid #93c5fd;background:#eff6ff}
.pager{display:grid;grid-template-columns:1fr 1fr;gap:16px;margin-top:32px;padding-top:24px;border-top:1px solid var(--line)}
.pager-card{display:block;text-decoration:none;border:1px solid var(--line);border-radius:16px;padding:16px 18px;background:#fff;color:inherit;box-shadow:0 6px 18px rgba(15,23,42,.04)}
.pager-card:hover{border-color:#bfdbfe;box-shadow:0 10px 22px rgba(15,23,42,.07)}
.pager-card.next{text-align:right}
.pager-label{display:block;font-size:12px;text-transform:uppercase;letter-spacing:.08em;color:var(--muted);margin-bottom:6px}
@media (max-width:960px){.layout{grid-template-columns:1fr}.sidebar{position:relative;height:auto}.content{padding:16px}.article{padding:22px}.hero-title{font-size:1.7rem}.pager{grid-template-columns:1fr}}