:root{
  --bg:#f8f7f4;
  --paper:#ffffff;
  --ink:#212f3b;
  --muted:#5d6d7c;
  --accent:#14607a;
  --accent-deep:#0d3b4f;
  --amber:#b45309;
  --violet:#6d28d9;
  --line:#e5e2da;
  --soft:#eef4f6;
  --serif:"Noto Serif SC","Source Han Serif SC","Songti SC",Georgia,"Times New Roman",serif;
  --sans:"Noto Sans SC","Source Han Sans SC","Segoe UI",-apple-system,"PingFang SC","Microsoft YaHei",sans-serif;
  --math:Georgia,"Times New Roman",serif;
  --mono:"JetBrains Mono",Consolas,"Courier New",monospace;
}
*{box-sizing:border-box;margin:0;padding:0}
html{scroll-behavior:smooth}
body{font-family:var(--sans);background:var(--bg);color:var(--ink);font-size:16px;line-height:1.75}
a{color:var(--accent);text-decoration:none}
a:hover{text-decoration:underline}
.container{max-width:1080px;margin:0 auto;padding:0 20px}

.site-header{position:sticky;top:0;z-index:50;background:rgba(255,255,255,.96);backdrop-filter:blur(6px);border-bottom:1px solid var(--line)}
.header-inner{display:flex;align-items:center;justify-content:space-between;gap:16px;min-height:60px}
.brand{display:flex;align-items:center;gap:10px;color:var(--ink)}
.brand:hover{text-decoration:none}
.brand-mark{display:inline-flex;align-items:center;justify-content:center;width:36px;height:36px;border-radius:9px;background:linear-gradient(135deg,var(--accent-deep),var(--accent));color:#fff;font-family:var(--math);font-size:22px;font-weight:700}
.brand-text{font-family:var(--serif);font-size:19px;font-weight:700;line-height:1.15}
.brand-text small{display:block;font-family:var(--sans);font-size:11px;font-weight:400;color:var(--muted);letter-spacing:.04em}
.site-nav{display:flex;flex-wrap:wrap;justify-content:flex-end;gap:2px}
.site-nav a{padding:6px 10px;border-radius:6px;font-size:.9rem;color:#3c4a58}
.site-nav a:hover{background:var(--soft);text-decoration:none;color:var(--accent)}
.site-nav a.active{background:var(--soft);color:var(--accent);font-weight:600}

.hero{background:linear-gradient(120deg,#0d3b4f 0%,#14607a 55%,#1d7d97 100%);background-image:linear-gradient(120deg,rgba(13,59,79,.97) 0%,rgba(20,96,122,.97) 55%,rgba(29,125,151,.97) 100%),linear-gradient(rgba(255,255,255,.05) 1px,transparent 1px),linear-gradient(90deg,rgba(255,255,255,.05) 1px,transparent 1px);background-size:auto,30px 30px,30px 30px;color:#eaf3f6;padding:72px 0 64px}
.hero-kicker{font-size:.8rem;letter-spacing:.28em;color:#9fd0de;margin-bottom:14px}
.hero h1{font-family:var(--serif);font-size:clamp(1.9rem,4.2vw,3rem);line-height:1.25;max-width:22em}
.hero-sub{margin-top:18px;max-width:40em;color:#c8dde5;font-size:1.02rem}
.hero-formula{font-family:var(--math);font-style:italic;font-size:1.25rem;color:#ffd9a8;margin-top:22px;letter-spacing:.02em}
.hero-actions{margin-top:28px;display:flex;gap:14px;flex-wrap:wrap}
.btn{display:inline-block;padding:10px 22px;border-radius:8px;font-size:.95rem;border:1px solid transparent;transition:.15s}
.btn-primary{background:#ffd9a8;color:#4a2f07;font-weight:600}
.btn-primary:hover{background:#ffcf8f;text-decoration:none}
.btn-ghost{border-color:rgba(255,255,255,.45);color:#eaf3f6}
.btn-ghost:hover{background:rgba(255,255,255,.1);text-decoration:none}

.section{padding:52px 0}
.section-alt{background:var(--paper);border-top:1px solid var(--line);border-bottom:1px solid var(--line)}
.section-title{font-family:var(--serif);font-size:1.55rem;margin-bottom:6px}
.section-sub{color:var(--muted);font-size:.95rem;margin-bottom:30px}

.card-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(240px,1fr));gap:18px}
.card{background:var(--paper);border:1px solid var(--line);border-radius:12px;padding:22px;transition:.18s}
.card:hover{border-color:#bcd3db;box-shadow:0 6px 18px rgba(13,59,79,.08);transform:translateY(-2px)}
.card h3{font-size:1.05rem;margin-bottom:8px}
.card p{font-size:.9rem;color:var(--muted)}
.card .card-icon{display:inline-flex;align-items:center;justify-content:center;width:38px;height:38px;border-radius:9px;background:var(--soft);color:var(--accent);font-family:var(--math);font-weight:700;font-size:19px;margin-bottom:12px}
.card .card-more{display:inline-block;margin-top:10px;font-size:.88rem}

.article{display:grid;grid-template-columns:230px minmax(0,1fr);gap:44px;padding-top:44px;padding-bottom:64px}
.toc{position:sticky;top:84px;align-self:start;font-size:.88rem}
.toc-title{font-weight:700;color:var(--muted);font-size:.8rem;letter-spacing:.1em;margin-bottom:10px}
.toc a{display:block;padding:5px 0 5px 12px;border-left:2px solid var(--line);color:#3c4a58}
.toc a:hover{color:var(--accent);border-left-color:var(--accent);text-decoration:none}
.page-title{font-family:var(--serif);font-size:2rem;line-height:1.3}
.page-meta{color:var(--muted);font-size:.88rem;margin:10px 0 6px;padding-bottom:18px;border-bottom:1px solid var(--line)}
article section{margin-top:34px}
article h2{font-family:var(--serif);font-size:1.35rem;padding-bottom:8px;border-bottom:1px solid var(--line);margin-bottom:14px}
article h3{font-size:1.08rem;margin:20px 0 8px}
article p{margin:10px 0}
article ul,article ol{margin:10px 0 10px 24px}
article li{margin:5px 0}
var,.m{font-family:var(--math);font-style:italic}
.math-block{font-family:var(--math);font-style:italic;text-align:center;font-size:1.18rem;margin:20px 0;letter-spacing:.01em}
.math-block sup,.math-block sub{font-style:normal}
.thm,.def,.rem{border-radius:8px;padding:14px 18px;margin:18px 0;font-size:.95rem}
.thm{background:#edf5f8;border-left:4px solid var(--accent)}
.def{background:#fbf4ea;border-left:4px solid var(--amber)}
.rem{background:#f3f1ec;border-left:4px solid var(--muted)}
.thm-title,.def-title,.rem-title{font-weight:700;font-family:var(--serif);margin-bottom:4px}
.fig{margin:24px 0;text-align:center}
.fig img{max-width:100%;border:1px solid var(--line);background:#fff;border-radius:8px;padding:10px}
.figcap{font-size:.85rem;color:var(--muted);margin-top:8px}
table.data{width:100%;border-collapse:collapse;margin:18px 0;font-size:.92rem;background:var(--paper)}
table.data th{background:#eff3f5;text-align:left;font-weight:600}
table.data th,table.data td{border:1px solid var(--line);padding:8px 12px;vertical-align:top}
code{font-family:var(--mono);font-size:.86em;background:#eef0ea;border-radius:4px;padding:1px 5px}
pre.block{font-family:var(--mono);font-size:.84rem;line-height:1.65;background:#f6f4ee;border:1px solid var(--line);border-radius:8px;padding:16px 18px;overflow-x:auto;margin:18px 0}
pre.block code{background:none;padding:0}
.refs{font-size:.9rem}
.refs li{margin:8px 0;color:#37444f}

.update-list{list-style:none;margin:0}
.update-list li{display:flex;gap:14px;padding:10px 0;border-bottom:1px dashed var(--line);font-size:.93rem}
.update-list .date{flex:0 0 92px;color:var(--muted);font-variant-numeric:tabular-nums}
.stats-band{display:grid;grid-template-columns:repeat(auto-fit,minmax(150px,1fr));gap:14px;text-align:center}
.stats-band .stat{background:var(--paper);border:1px solid var(--line);border-radius:10px;padding:18px 10px}
.stat b{display:block;font-family:var(--math);font-size:1.7rem;color:var(--accent)}
.stat span{font-size:.85rem;color:var(--muted)}

.video-card{background:var(--paper);border:1px solid var(--line);border-radius:12px;padding:18px;margin-bottom:26px}
.video-head{display:flex;align-items:baseline;justify-content:space-between;gap:12px;flex-wrap:wrap;margin-bottom:6px}
.video-head h3{font-size:1.05rem}
.video-head .ep{color:var(--muted);font-size:.85rem}
.video-desc{font-size:.9rem;color:var(--muted);margin-bottom:12px}
.ratio{position:relative;width:100%;padding-bottom:56.25%;border-radius:8px;overflow:hidden;background:#0b1620}
.ratio iframe{position:absolute;inset:0;width:100%;height:100%;border:0}

.demo-panel{background:var(--paper);border:1px solid var(--line);border-radius:12px;padding:22px;margin:18px 0}
.demo-controls{display:flex;flex-wrap:wrap;gap:18px;margin:14px 0}
.ctrl{display:flex;align-items:center;gap:10px;font-size:.9rem}
.ctrl label{font-family:var(--math);font-style:italic;font-weight:700;width:26px;text-align:center}
.ctrl input[type=range]{width:140px;accent-color:var(--accent)}
.readout{font-family:var(--math);font-style:italic;font-size:1.02rem;background:#edf5f8;border-radius:8px;padding:10px 16px;margin-top:10px;display:inline-block}
canvas.demo-canvas{max-width:100%;width:100%;background:#fdfdfc;border:1px solid var(--line);border-radius:8px;touch-action:pan-y}
.btn-small{display:inline-block;padding:7px 16px;border-radius:7px;border:1px solid var(--accent);color:var(--accent);background:#fff;font-size:.88rem;cursor:pointer;transition:.15s}
.btn-small:hover{background:var(--soft)}
.btn-small.primary{background:var(--accent);color:#fff}
.btn-small.primary:hover{background:var(--accent-deep)}

.site-footer{background:#14212b;color:#8fa3b0;margin-top:30px;padding:34px 0;font-size:.88rem}
.site-footer p{margin:4px 0}
.site-footer a{color:#9fd0de}

@media (max-width:900px){
  .article{display:block}
  .toc{display:none}
  .header-inner{flex-direction:column;align-items:flex-start;padding:10px 0}
  .site-nav{justify-content:flex-start}
  .hero{padding:52px 0 46px}
}

.article-single{max-width:860px;padding-top:44px;padding-bottom:64px}
.yt-facade{position:absolute;inset:0;width:100%;height:100%;border:0;padding:0;cursor:pointer;background:linear-gradient(135deg,#0d2231 0%,#123c50 60%,#155e75 100%);display:flex;flex-direction:column;align-items:center;justify-content:center;gap:14px;color:#eaf3f6;font-family:var(--sans);font-size:.88rem}
.yt-facade:hover{background:linear-gradient(135deg,#0f2838 0%,#15465e 60%,#1a6c8a 100%)}
.yt-play{display:inline-flex;align-items:center;justify-content:center;width:66px;height:66px;border-radius:50%;background:rgba(255,217,168,.95);color:#4a2f07;font-size:25px;padding-left:6px;box-shadow:0 8px 24px rgba(0,0,0,.35);transition:transform .15s}
.yt-facade:hover .yt-play{transform:scale(1.07)}
.yt-hint{opacity:.72;letter-spacing:.02em;text-align:center;padding:0 16px}