:root{--bg:#09090b;--p:#141418;--p2:#1a1a20;--line:#2a2a33;--t:#eeeef2;--m:#a2a2b0;--b:#78a5ff;--r:#ff646e;--y:#f1c84b;--g:#55d69a;--o:#ff8748}*{box-sizing:border-box}body{margin:0;background:var(--bg);color:var(--t);font:16px/1.72 Inter,system-ui,-apple-system,"Segoe UI",sans-serif}main{width:min(100%,1680px);max-width:none;margin:auto;padding:30px clamp(24px,4.5vw,72px) 70px}h1,h2{font-family:Georgia,serif;line-height:1.2;letter-spacing:-.02em}h1{font-size:clamp(2.3rem,5vw,3.6rem);margin:.3em 0 .5em}h2{font-size:clamp(1.55rem,3vw,2rem);margin:0}h3{margin:0 0 10px;line-height:1.35}p{margin:12px 0}.muted{color:var(--m)}.intro{font-size:1.15rem;color:#b9bfd0;max-width:800px}.eyebrow,.tag{display:inline-block;border:1px solid #63343a;background:#211316;color:var(--r);border-radius:8px;padding:5px 11px;font-size:.75rem;font-weight:800;letter-spacing:.12em;text-transform:uppercase}.meta{display:flex;flex-wrap:wrap;gap:18px;color:var(--m);font-size:.88rem;margin:22px 0 34px}.dot{display:inline-block;width:8px;height:8px;background:var(--r);border-radius:50%;margin-right:7px}.notice,.tip,.warn,.good{border:1px solid var(--line);border-radius:13px;padding:16px 19px;margin:20px 0;background:var(--p)}.notice{border-color:#663136;background:#1e1215}.notice strong{color:var(--r)}.tip{border-color:#34496b;background:#111722}.tip strong{color:var(--b)}.warn{border-color:#6b5522;background:#1b180f}.warn strong{color:var(--y)}.good{border-color:#28583f;background:#101b15}.good strong{color:var(--g)}.section{margin-top:62px}.head{display:flex;gap:13px;align-items:center;margin-bottom:18px}.tag.blue{color:var(--b);border-color:#34496b;background:#111722}.tag.yellow{color:var(--y);border-color:#6b5522;background:#1b180f}.tag.green{color:var(--g);border-color:#28583f;background:#101b15}.cards{display:grid;grid-template-columns:repeat(auto-fit,minmax(210px,1fr));gap:13px;margin:20px 0}.card,.step,.quizbox{border:1px solid var(--line);border-radius:14px;background:var(--p);padding:19px}.card .k{font-size:.7rem;color:var(--m);letter-spacing:.15em;text-transform:uppercase}.card h3{margin:8px 0}.card p{color:var(--m);margin:4px 0}.step{margin:18px 0;padding:22px;background:linear-gradient(145deg,#141418,#101014)}.stitle{display:flex;gap:12px;align-items:flex-start;margin-bottom:10px}.num{display:grid;place-items:center;min-width:34px;height:34px;background:#251619;border:1px solid #63343a;border-radius:9px;color:var(--r);font-weight:900}.code{border:1px solid #292932;border-radius:11px;overflow:hidden;margin:14px 0;background:#0e0e12}.codehead{padding:8px 13px;border-bottom:1px solid #292932;color:#9696a5;font-size:.7rem;letter-spacing:.15em;text-transform:uppercase}.code pre{margin:0;padding:14px 16px;overflow:auto;white-space:pre-wrap;overflow-wrap:anywhere;color:#8db4ff;font: .9rem/1.7 ui-monospace,Consolas,monospace}.inline{font:.92em ui-monospace,Consolas,monospace;color:#8db4ff;background:#202027;border:1px solid #2b2b35;padding:2px 5px;border-radius:5px;overflow-wrap:anywhere}.tree{color:#ff9a61}.tablewrap{overflow:auto;border:1px solid var(--line);border-radius:11px;margin:16px 0}table{width:100%;border-collapse:collapse;min-width:520px;background:#101014}td,th{padding:11px 13px;text-align:left;vertical-align:top;border-bottom:1px solid var(--line)}th{background:#1a1a20;color:var(--m);font-size:.75rem;letter-spacing:.08em;text-transform:uppercase}tr:last-child td{border-bottom:0}.check{list-style:none;padding:0}.check li{padding-left:27px;position:relative;margin:8px 0}.check li:before{content:"□";position:absolute;left:2px;color:var(--b);font-size:1.2rem}.quizbox{padding:23px}.qtop{display:flex;justify-content:space-between;gap:12px;color:var(--m);font-size:.78rem;letter-spacing:.1em;text-transform:uppercase}.progress{height:5px;background:#292930;border-radius:20px;margin:13px 0 22px;overflow:hidden}.fill{height:100%;width:0;background:var(--o);transition:width .2s}.question{font-size:1.15rem;font-weight:750;line-height:1.5;margin:12px 0 18px}.answers{display:grid;gap:9px}.answer{display:flex;align-items:center;gap:12px;text-align:left;width:100%;border:1px solid var(--line);border-radius:10px;padding:12px;background:#19191f;color:var(--t);font:inherit;cursor:pointer}.answer:hover{border-color:#555567}.answer:focus-visible,.btn:focus-visible{outline:2px solid var(--b);outline-offset:3px}.letter{display:grid;place-items:center;min-width:26px;height:26px;border-radius:50%;background:#292930;font-size:.8rem;font-weight:800}.answer.selected{border-color:var(--b);background:#151d2b}.answer.correct{border-color:var(--g);background:#102219}.answer.incorrect{border-color:var(--r);background:#261417}.feedback{display:none;padding:14px;margin-top:15px;border:1px solid var(--line);border-radius:10px;background:#101014}.feedback.show{display:block}.feedback.good{border-color:#28583f}.feedback.bad{border-color:#663136}.actions{display:flex;flex-wrap:wrap;gap:10px;margin-top:17px}.btn{border:1px solid var(--line);border-radius:9px;padding:10px 15px;background:transparent;color:var(--t);font-weight:800;cursor:pointer}.btn.primary{background:#ff6d2e;border-color:#ff6d2e;color:white}.btn:disabled{opacity:.4;cursor:not-allowed}.result{display:none}.result.show{display:block}.score{font-size:2.2rem;color:var(--o);font-weight:900}.foot{border-top:1px solid var(--line);margin-top:60px;padding-top:22px;color:var(--m);font-size:.9rem}@media(max-width:620px){main{padding:20px 14px 50px}.step,.quizbox{padding:16px}.head{align-items:flex-start}}@media print{body{background:white;color:#111}main{max-width:none;padding:0}.step,.card,.quizbox,.notice,.tip,.warn,.good{background:white;color:#111;break-inside:avoid}.muted,.card p,.foot{color:#444}.actions{display:none}}
/* Mobile: keep lesson navigation and quiz controls easy to tap. */
@media(max-width:620px){
  .toc a{display:inline-flex;align-items:center;min-height:44px;padding:9px 10px;line-height:1.4}
  .btn{min-height:44px}
  .answer{min-height:48px}
  .head .tag{flex:none}
}.lesson-nav{display:flex;align-items:stretch;justify-content:space-between;gap:14px;margin-top:34px;padding:16px;border:1px solid var(--line);border-radius:14px;background:var(--p)}
.lesson-nav a{color:var(--t);text-decoration:none}
.lesson-nav-prev,.lesson-nav-next{display:flex;flex:1;flex-direction:column;justify-content:center;gap:4px;min-height:58px;padding:10px 14px;border:1px solid var(--line);border-radius:10px;background:var(--p2)}
.lesson-nav-prev span,.lesson-nav-next span{color:var(--m);font-size:.72rem;font-weight:800;letter-spacing:.08em;text-transform:uppercase}
.lesson-nav-prev strong,.lesson-nav-next strong{font-size:.92rem;line-height:1.4}

.lesson-nav a:hover{border-color:var(--r)}
.lesson-nav a:focus-visible{outline:2px solid var(--b);outline-offset:3px}
@media(max-width:620px){.lesson-nav{flex-direction:column;padding:12px}.lesson-nav-prev,.lesson-nav-next{flex:none;width:100%;min-height:64px}}
.course-trail{display:flex;align-items:center;gap:11px;margin-bottom:20px;color:var(--m);font-size:.84rem}
.course-trail a{display:inline-flex;align-items:center;min-height:44px;color:var(--r)!important;font-weight:800;text-decoration:none}
.course-trail a:hover{text-decoration:underline;text-underline-offset:4px}
.course-trail span{padding-left:11px;border-left:1px solid var(--line)}
.course-trail a:focus-visible{outline:2px solid var(--b);outline-offset:3px;border-radius:4px}
@media(max-width:620px){.course-trail{flex-wrap:wrap;gap:7px;margin-bottom:16px}.course-trail a{min-height:44px}}
.lesson-figure{margin:18px 0 24px;padding:10px;border:1px solid var(--line);border-radius:14px;background:var(--p)}
.lesson-figure img{display:block;width:100%;height:auto;max-height:720px;object-fit:contain;border-radius:8px;background:var(--bg)}
.lesson-figure figcaption{margin:10px 4px 2px;color:var(--m);font-size:.92rem;line-height:1.6}

.lesson-diagram{margin:20px 0 24px;padding:16px;border:1px solid var(--line);border-radius:14px;background:var(--p)}.lesson-diagram .flow{display:flex;flex-wrap:wrap;gap:10px;align-items:stretch;justify-content:center}.lesson-diagram .flowitem{flex:1 1 170px;border:1px solid var(--line);border-radius:12px;background:var(--p2);padding:15px;color:var(--m);line-height:1.5}.lesson-diagram .flowitem strong{display:block;margin-bottom:6px;color:var(--b)}.lesson-diagram .arrow{display:grid;place-items:center;flex:0 1 auto;color:var(--o);font-size:.9rem;font-weight:800}.lesson-diagram figcaption{margin-top:13px;color:var(--m);font-size:.9rem;line-height:1.55}
@media print{.lesson-diagram,.lesson-diagram .flowitem{background:white;color:#111;break-inside:avoid}.lesson-diagram figcaption{color:#444}}