:root{
  --page-w: 850px;
  --brand:#0ea5e9;
  --ink:#0f172a;
  --muted:#475569;
  --bg:#ffffff;
  --paper:#f8fafc;
  --radius:14px;
}

html{scroll-behavior:smooth}
body{
  margin:0;
  font-family: ui-sans-serif, system-ui, -apple-system, Segoe UI, Roboto, Noto Sans, Helvetica, Arial;
  color:var(--ink);
  background:linear-gradient(180deg,#f0f9ff 0,#ffffff 300px);
}

/* Topbar */
.topbar{
  position:sticky; top:0; z-index:50;
  backdrop-filter: saturate(1.2) blur(6px);
  background:rgba(255,255,255,.8);
  border-bottom:1px solid #e2e8f0;
}
.topbar-inner{display:flex;gap:12px;align-items:center;justify-content:space-between;max-width:var(--page-w);margin:auto;padding:10px 16px}
.brand-link{display:flex;gap:10px;align-items:center;text-decoration:none;color:inherit}
.brand-text{font-weight:800;font-size:16px}
@media (min-width:981px){ .brand-text{font-size:22px} }

.btn{appearance:none;border:1px solid #e2e8f0;border-radius:999px;padding:10px 14px;font-weight:600;cursor:pointer;background:#fff}
.btn.primary{background:var(--brand);border-color:var(--brand);color:#fff}
.btn:active{transform:translateY(1px)}
@media (max-width:980px){ .btn{padding:8px 10px;font-size:13px} }

/* Layout */
.wrap{max-width:var(--page-w);margin:18px auto;padding:0 16px 64px}
.doc{
  background:var(--bg);
  border:1px solid #e2e8f0;
  border-radius:var(--radius);
  box-shadow:0 10px 30px rgba(2,6,23,.06);
  overflow:hidden;
}
header.doc-head{
  background:radial-gradient(1200px 300px at 10% -10%, #e0f2fe 0, transparent 70%);
  padding:28px 28px 12px 28px;
}
.eyebrow{color:var(--brand);font-weight:800;letter-spacing:.02em;margin:0 0 8px}
h1.title{font-size:clamp(22px,3vw,32px);line-height:1.25;margin:0}
.meta{display:flex;gap:18px;flex-wrap:wrap;color:var(--muted);margin-top:10px;font-size:14px}

.body{
  display:grid;
  grid-template-columns:260px 1fr;
  gap:24px;
  padding:20px;
  align-items:flex-start;
}
@media (max-width:980px){ .body{grid-template-columns:1fr} }

/* TOC */
.toc{
  position:sticky;
  top:76px;
  align-self:flex-start;
  background:var(--paper);
  border:1px solid #e2e8f0;
  border-radius:12px;
  padding:14px;
  margin-top:0;
}
.toc h3{
  margin:0 0 8px;
  font-size:14px;
  letter-spacing:.02em;
  color:var(--muted);
  display:flex; justify-content:space-between; align-items:center;
  cursor:pointer;
}
.toc h3 .arrow{ font-size:12px; transition:transform .2s; }
.toc.open h3 .arrow{ transform:rotate(180deg); }
.toc ul{ margin:0; padding-left:18px; list-style-type:disc; }
.toc li{ margin:6px 0; }
.toc a{ color:inherit; text-decoration:none }
.toc a:hover{ color:var(--brand) }

@media (min-width:981px){
  .toc h3 .arrow{ display:none }
  .toc h3{ cursor:default }
}

/* TOC mobile hide/show */
@media (max-width:980px) {
  .toc ul {
    display: none;
  }
  .toc.open ul {
    display: block;
  }
}

/* Article */
article{min-height:40vh}
article h2:first-of-type{margin-top:0;}
article h2{margin-top:28px; font-size:22px}
article h3{margin-top:18px; font-size:18px}
p{line-height:1.7}
.lead{font-size:17px;color:#334155;margin-top:0}
.figure{margin:18px 0; border:1px solid #e2e8f0; border-radius:12px; overflow:hidden; background:#fff}
.figure img{width:100%; display:block}
.figcap{font-size:13px; color:var(--muted); padding:8px 12px; background:#f8fafc}
.callout{border-left:4px solid var(--brand); background:#f0f9ff; padding:12px 14px; border-radius:8px}
.video-thumb{position:relative; display:block; border-radius:12px; overflow:hidden; border:1px solid #e2e8f0}
.video-thumb img{display:block; width:100%; height:auto}
.play{position:absolute; inset:0; display:grid; place-items:center;}
.play svg{width:76px; height:76px; filter:drop-shadow(0 2px 8px rgba(0,0,0,.35));}
.kbd{font-family:ui-monospace, SFMono-Regular, Menlo, monospace; background:#e2e8f0; padding:.1em .4em; border-radius:6px}
.page-break{break-after:page}

@media print{
  @page{ size: A4; margin: 14mm; }
  body{ background:#fff }
  .topbar{ display:none }
  .wrap{ padding:0; margin:0 }
  .doc{ border:none; box-shadow:none; border-radius:0 }
  .body{ display:block; padding:0 }
  .toc{ page-break-inside:avoid; position:static; background:#fff }
  a[href^="http"]:after{ content:" (" attr(href) ")"; font-size:80%; color:#475569 }
}

.ad{ text-align:center; margin:20px 0; }
@media (min-width:981px){
  .desktop-only{ display:block; }
  .mobile-only{ display:none; }
}
@media (max-width:980px){
  .desktop-only{ display:none; }
  .mobile-only{ display:block; }
}

.phone-only{ display:none; }
.tablet-only{ display:none; }
@media (max-width:767px){ .phone-only{ display:block; } }
@media (min-width:768px) and (max-width:980px){ .tablet-only{ display:block; } }

.ad-siderail{ position:fixed; top:150px; z-index:30; display:none; }
@media (min-width:1200px){
  .ad-siderail{ display:block; }
  .ad-siderail.left{ left: calc(50% - (var(--page-w) / 2) - 180px); }
  .ad-siderail.right{ right: calc(50% - (var(--page-w) / 2) - 180px); }
}

.ad-728x90-bottom{ text-align:center; margin:30px 0; }
.ad-728x90-bottom .ad-728x90{ display:inline-block; }

@media (min-width:1200px){
  body{ padding-left:180px; padding-right:180px; }
}