:root{
  --blue:#1a5cf0;
  --cyan:#0090c8;
  --green:#00a878;
  --ink:#0f172a;
  --text:#33415c;
  --muted:#8593ab;
  --line:#eaf0fa;
  --panel:#fbfcfe;
  --mono:ui-monospace,SFMono-Regular,Menlo,Consolas,"Courier New",monospace;
}
*,*::before,*::after{box-sizing:border-box}
html{-webkit-text-size-adjust:100%}
body{
  margin:0;background:#fff;color:var(--text);
  font:16px/1.85 -apple-system,BlinkMacSystemFont,"PingFang SC","Hiragino Sans GB","Microsoft YaHei",sans-serif;
  -webkit-font-smoothing:antialiased;
}
a{color:inherit}
img{max-width:100%}
.wrap{max-width:1080px;margin:0 auto;padding:0 20px}

/* ---------- header ---------- */
.hd{position:sticky;top:0;z-index:30;background:rgba(255,255,255,.88);
  -webkit-backdrop-filter:saturate(180%) blur(12px);backdrop-filter:saturate(180%) blur(12px);
  border-bottom:1px solid var(--line)}
.hd .wrap{display:flex;align-items:center;gap:22px;height:64px}
.brand{display:flex;align-items:center;gap:10px;text-decoration:none;color:var(--ink);
  font-weight:700;font-size:17px;letter-spacing:.5px;white-space:nowrap}
.brand svg{width:27px;height:27px;flex:none}
.brand em{font-style:normal;font-family:var(--mono);font-size:10.5px;color:#9aa8bf;
  border-left:1px solid var(--line);padding-left:10px;margin-left:2px;letter-spacing:.6px;font-weight:400}
.nav{display:flex;gap:22px;margin-left:auto;font-size:14px}
.nav a{text-decoration:none;color:#5a6b88;padding:5px 0;transition:color .16s}
.nav a:hover{color:var(--blue)}

/* ---------- hero ---------- */
.hero{position:relative;border-bottom:1px solid var(--line);overflow:hidden;
  background:linear-gradient(180deg,#fbfdff 0%,#fff 100%)}
.hero::before{content:"";position:absolute;inset:0;pointer-events:none;
  background-image:linear-gradient(#eef4ff 1px,transparent 1px),linear-gradient(90deg,#eef4ff 1px,transparent 1px);
  background-size:64px 64px;
  -webkit-mask-image:radial-gradient(120% 95% at 18% -10%,#000 0%,transparent 70%);
  mask-image:radial-gradient(120% 95% at 18% -10%,#000 0%,transparent 70%)}
.hero .wrap{position:relative;padding:32px 20px 30px}
.crumb{font-size:13px;color:var(--muted);margin-bottom:14px}
.crumb a{text-decoration:none;color:var(--muted);transition:color .16s}
.crumb a:hover{color:var(--blue)}
.crumb i{font-style:normal;margin:0 8px;color:#cbd6e8}
h1{margin:0 0 15px;font-size:31px;line-height:1.42;color:var(--ink);font-weight:700;letter-spacing:.2px}
.meta{display:flex;flex-wrap:wrap;gap:8px}
.chip{font-family:var(--mono);font-size:11.5px;color:#5a6b88;background:#f4f8ff;
  border:1px solid #e4edfd;border-radius:999px;padding:4px 11px;letter-spacing:.3px}
.chip.acc{color:var(--blue);border-color:#d6e4ff;background:#eef4ff}
.chip.dot::before{content:"";display:inline-block;width:5px;height:5px;border-radius:50%;
  background:var(--green);margin-right:7px;vertical-align:1px}

/* ---------- article ---------- */
.main{padding:38px 0 6px}
.col{max-width:800px;margin:0 auto;padding:0 20px}
.doc p{margin:0 0 18px;font-size:16.5px;line-height:1.95;color:var(--text);text-align:justify}
.doc .lead{position:relative;font-size:17.5px;line-height:1.9;color:#243b5c;padding-left:18px;margin-bottom:24px}
.doc .lead::before{content:"";position:absolute;left:0;top:6px;bottom:6px;width:3px;border-radius:2px;
  background:linear-gradient(180deg,var(--blue),var(--green))}
.doc h2{margin:34px 0 14px;font-size:19.5px;line-height:1.55;color:var(--ink);font-weight:700;
  display:flex;gap:10px;align-items:baseline}
.doc h2 em{font-style:normal;font-family:var(--mono);font-size:11.5px;font-weight:500;color:var(--blue);
  background:#eef4ff;border:1px solid #dfeaff;border-radius:6px;padding:1px 7px;flex:none;transform:translateY(-1px)}
figure{margin:26px 0;border:1px solid var(--line);border-radius:14px;overflow:hidden;background:#f7f9fc}
figure img{display:block;width:100%;height:auto;max-height:400px;object-fit:cover}
figcaption{font-family:var(--mono);font-size:12px;color:var(--muted);padding:10px 14px;
  border-top:1px solid var(--line);letter-spacing:.3px}

/* ---------- qa ---------- */
.qa{margin:28px 0 4px;border:1px solid var(--line);border-radius:14px;background:var(--panel);padding:4px 20px}
.qa .qh{padding:15px 0 6px;font-weight:600;color:var(--ink);font-size:15.5px;line-height:1.6}
.qa .qb{padding:0 0 15px;color:#4a5b78;font-size:15px;line-height:1.85;border-bottom:1px dashed #e7eefb}
.qa .qb:last-child{border-bottom:0}

/* ---------- link sections ---------- */
.sec{padding:46px 0 6px}
.sec-h{display:flex;align-items:center;gap:12px;margin-bottom:18px}
.sec-h h2{margin:0;font-size:18.5px;color:var(--ink);font-weight:700;white-space:nowrap}
.sec-h i{flex:1;height:1px;background:linear-gradient(90deg,#e0ebff,transparent)}
.sec-h b{font-family:var(--mono);font-size:11px;color:var(--blue);font-weight:500;letter-spacing:.5px}
.links{display:grid;grid-template-columns:1fr 1fr;gap:10px 16px}
.links a{display:flex;align-items:baseline;gap:9px;padding:11px 14px;border:1px solid var(--line);
  border-radius:10px;background:var(--panel);text-decoration:none;color:#33415c;font-size:14.5px;
  line-height:1.6;transition:transform .16s,border-color .16s,box-shadow .16s,color .16s,background .16s}
.links a:hover{transform:translateY(-2px);border-color:#cfe0ff;background:#fff;color:var(--blue);
  box-shadow:0 12px 26px -14px rgba(26,92,240,.5)}
.links a u{text-decoration:none;font-family:var(--mono);font-size:10.5px;color:#a8b6cc;flex:none}
.frd{display:flex;flex-wrap:wrap;gap:8px}
.frd a{font-size:13px;color:#5a6b88;text-decoration:none;border:1px solid var(--line);
  background:var(--panel);border-radius:999px;padding:6px 14px;transition:.16s}
.frd a:hover{color:var(--blue);border-color:#cfe0ff;background:#fff}

/* ---------- home ---------- */
.home-hero{padding:56px 0 40px}
.home-hero h1{font-size:38px;letter-spacing:1px}
.home-hero .sub{max-width:640px;font-size:16px;color:#4a5b78;line-height:1.9;margin:0 0 22px}
.stat{display:flex;flex-wrap:wrap;gap:26px;margin-top:24px}
.stat div{font-family:var(--mono)}
.stat span{display:block;font-size:26px;color:var(--blue);font-weight:600;letter-spacing:-.5px}
.stat small{font-size:11.5px;color:var(--muted);letter-spacing:.6px}
.cats{display:grid;grid-template-columns:repeat(4,1fr);gap:12px;padding:8px 0 4px}
.cats a{display:block;padding:16px;border:1px solid var(--line);border-radius:12px;background:var(--panel);
  text-decoration:none;color:var(--ink);font-size:15px;font-weight:600;transition:.16s;position:relative;overflow:hidden}
.cats a:hover{transform:translateY(-2px);border-color:#cfe0ff;background:#fff;color:var(--blue);
  box-shadow:0 12px 26px -14px rgba(26,92,240,.45)}
.cats a small{display:block;font-family:var(--mono);font-size:10.5px;color:var(--muted);
  font-weight:400;margin-top:4px;letter-spacing:.4px}

/* ---------- footer ---------- */
.ft{margin-top:60px;border-top:1px solid var(--line);background:var(--panel)}
.ft .wrap{padding:26px 20px 32px;font-size:12.5px;color:var(--muted);
  display:flex;flex-wrap:wrap;gap:10px 20px;justify-content:space-between;line-height:1.9}
.ft b{color:#5a6b88;font-weight:600}
.ft .wrap>div a{color:#5a6b88;text-decoration:none;border-bottom:1px solid #cdd9ec}
.ft .wrap>div a:hover{color:var(--blue);border-bottom-color:var(--blue)}
.ft nav{display:flex;gap:16px;flex-wrap:wrap}
.ft nav a{text-decoration:none;color:var(--muted)}
.ft nav a:hover{color:var(--blue)}

@media(max-width:840px){
  .cats{grid-template-columns:repeat(2,1fr)}
  .home-hero h1{font-size:30px}
}
@media(max-width:760px){
  .nav{display:none}
  h1{font-size:22px}
  .hero .wrap{padding:22px 20px 20px}
  .main{padding:26px 0 4px}
  .doc p{font-size:16px;line-height:1.9}
  .doc .lead{font-size:16.5px}
  .doc h2{font-size:18px;margin:28px 0 12px}
  .links{grid-template-columns:1fr}
  .sec{padding:34px 0 4px}
  .hd .wrap{height:56px}
}

/* ---------- refinements ---------- */
.links a{border-color:#e5edfa}
.links a u{color:#9aabc4}
.home-hero{padding-right:360px}
.home-deco{position:absolute;right:34px;top:50%;transform:translateY(-50%);width:272px;
  pointer-events:none}
@media(max-width:1000px){
  .home-hero{padding-right:20px}
  .home-deco{display:none}
}

/* ---------- long-form additions ---------- */
.doc h2{scroll-margin-top:84px}
.toc{margin:26px 0 6px;border:1px solid #e5edfa;border-radius:14px;background:#fbfcfe;padding:15px 18px 13px}
.toc h4{margin:0 0 9px;font-size:11.5px;color:#8593ab;font-family:var(--mono);font-weight:500;letter-spacing:1.2px}
.toc ol{margin:0;padding:0;list-style:none;display:grid;grid-template-columns:1fr;gap:1px}
.toc a{display:flex;gap:10px;text-decoration:none;color:#33415c;font-size:14px;line-height:1.85}
.toc a:hover{color:#1a5cf0}
.toc a u{text-decoration:none;font-family:var(--mono);font-size:10.5px;color:#a8b6cc;flex:none;padding-top:1px}
.tips{margin:24px 0 6px;padding:0;list-style:none;display:grid;grid-template-columns:1fr 1fr;gap:8px 22px}
.tips li{position:relative;padding-left:17px;font-size:15px;line-height:1.8;color:#33415c}
.tips li::before{content:"";position:absolute;left:0;top:.74em;width:6px;height:6px;border-radius:50%;
  background:linear-gradient(135deg,#1a5cf0,#00a878)}
.glossary{width:100%;border-collapse:collapse;margin:6px 0 4px;font-size:14.5px}
.glossary th{text-align:left;font-weight:600;color:#0f172a;font-size:12px;letter-spacing:.8px;
  padding:0 0 8px;border-bottom:1px solid #e5edfa}
.glossary td{padding:9px 0;border-bottom:1px dashed #eaf0fa;vertical-align:top;color:#4a5b78;line-height:1.8}
.glossary td:first-child{width:92px;font-weight:600;color:#1d4ed8;white-space:nowrap}
.endnote{margin:30px 0 0;padding:16px 18px;border-radius:12px;border:1px solid #e5edfa;
  background:linear-gradient(180deg,#f4f8ff,#fff);font-size:16px;color:#33415c;line-height:1.95}
@media(max-width:760px){
  .toc ol,.tips{grid-template-columns:1fr}
  .glossary td:first-child{width:76px}
  .endnote{font-size:15.5px}
}