:root{--ink:#1f2935;--mut:#6b7785;--line:#e6eaef;--accent:#2b5278;--green:#6AA84F;--amber:#b06a00}
*{box-sizing:border-box}
body{margin:0;font-family:-apple-system,"Segoe UI",Roboto,Arial,sans-serif;background:#f4f6f9;color:var(--ink)}
a{color:var(--accent)}
.hero{background:linear-gradient(135deg,#17212b,#243447);color:#fff;padding:34px 28px}
.hero .kick{color:#8fb6e0;font-size:13px;letter-spacing:1px;text-transform:uppercase;font-weight:700}
.hero h1{margin:6px 0 4px;font-size:28px}
.hero p{margin:0;color:#b9c6d3;font-size:14px}
.wrap{max-width:920px;margin:0 auto;padding:26px 22px 60px}
.secttl{font-size:13px;text-transform:uppercase;letter-spacing:.6px;color:var(--mut);font-weight:700;margin:24px 0 12px;display:flex;align-items:center;gap:8px}
.secttl:before{content:"";width:18px;height:2px;background:var(--green)}
.grid{display:grid;grid-template-columns:1fr 1fr;gap:14px}
.card{background:#fff;border:1px solid var(--line);border-radius:12px;padding:16px 18px;text-decoration:none;color:inherit;transition:.15s;display:block}
.card:hover{border-color:var(--accent);box-shadow:0 4px 14px rgba(20,40,70,.08)}
.card .n{color:var(--accent);font-weight:700;font-size:12px;letter-spacing:.5px}
.card .t{font-weight:600;font-size:15px;margin:4px 0 6px;line-height:1.3}
.card .d{color:var(--mut);font-size:12.5px;line-height:1.45}
.card .tags{margin-top:9px}
.tag{display:inline-block;background:#eef3f8;color:#3d5b7a;font-size:11px;padding:2px 8px;border-radius:20px;margin:2px 4px 0 0}
.srcgrp{font-size:13px;font-weight:600;color:#3d5b7a;margin:14px 0 8px}
.ext{display:flex;gap:10px;align-items:center;padding:13px 16px;background:#fff;border:1px solid var(--line);border-radius:10px;text-decoration:none;color:inherit;margin-bottom:8px}
.ext:hover{border-color:var(--accent);box-shadow:0 4px 14px rgba(20,40,70,.08)}
.ext .ic{flex:0 0 auto;width:34px;height:34px;border-radius:7px;background:#eef3f8;display:flex;align-items:center;justify-content:center;font-weight:700;color:#3d5b7a;font-size:12px}
.ext .et{font-weight:600;font-size:14px;line-height:1.3}
.ext .es{color:var(--mut);font-size:12px;margin-top:2px}
.foot{color:var(--mut);font-size:12px;margin-top:30px;border-top:1px solid var(--line);padding-top:14px}
/* lesson page */
.bar{background:#17212b;color:#fff;padding:11px 20px;font-size:13px;display:flex;gap:8px;align-items:center;flex-wrap:wrap}
.bar a{color:#8fb6e0;text-decoration:none}
.bar .sep{color:#46586a}
.wrap .meta{color:var(--mut);font-size:13px;font-weight:600;letter-spacing:.4px}
.wrap h1{font-size:26px;margin:6px 0 16px;line-height:1.25}
.toc-side{background:#fff;border:1px solid var(--line);border-radius:10px;padding:14px 18px;margin:0 0 24px}
.toc-side b{font-size:12px;text-transform:uppercase;color:var(--mut);letter-spacing:.5px;display:block;margin-bottom:6px}
.toc-side a{display:block;color:var(--accent);text-decoration:none;font-size:13.5px;padding:3px 0}
.toc-side a:hover{text-decoration:underline}
.lesson{font-size:15px;line-height:1.62;max-width:740px}
.lesson h2{font-size:20px;margin:30px 0 10px;padding-top:6px;scroll-margin-top:14px}
.lesson h3{font-size:16px;margin:20px 0 8px}
.lesson p{font-size:15px;line-height:1.62}
.lesson ul,.lesson ol{padding-left:22px}
.lesson li{margin:6px 0}
.lesson table{border-collapse:collapse;width:100%;margin:14px 0;font-size:14px}
.lesson th,.lesson td{border:1px solid var(--line);padding:8px 11px;text-align:left}
.lesson th{background:#f4f6f9;font-weight:600}
.lesson blockquote{margin:16px 0;padding:11px 16px;background:#fffaf0;border-left:3px solid var(--amber);color:#5b4a2c;font-style:italic;border-radius:0 8px 8px 0;font-size:14px}
.lesson blockquote p{margin:6px 0;font-size:14px}
.lesson code{background:#eef1f5;padding:1px 5px;border-radius:4px;font-size:13px}
.lesson hr{border:none;border-top:1px solid var(--line);margin:24px 0}
.apply{background:#f0f5ff;border:1px solid #cdddf3;border-radius:10px;padding:16px 20px;margin:26px 0 0;max-width:740px}
.apply h3{margin:0 0 8px;color:#2b5278;font-size:15px}
.apply ul{margin:0;padding-left:20px}
.apply li{margin:7px 0;font-size:14px;line-height:1.5}
.apply code{background:#e4ecf7}
.back{display:inline-block;margin-top:24px;color:var(--accent);text-decoration:none;font-weight:600}
@media(max-width:640px){.grid{grid-template-columns:1fr}}