*,*::before,*::after{box-sizing:border-box}
:root{
  --ink:#000;
  --paper:#fff;
  --hair:rgba(0,0,0,.16);
  --muted:rgba(0,0,0,.66);
  --r:18px;
  --pad:clamp(1rem,4vw,2.5rem);
  --mono:"Fira Code",ui-monospace,SFMono-Regular,Menlo,"Courier New",monospace;
  --sans:"Fira Sans",system-ui,-apple-system,"Segoe UI",Roboto,"Helvetica Neue",Arial,"Noto Sans SC",sans-serif;
}
html{scroll-behavior:smooth;-webkit-text-size-adjust:100%}
body{margin:0;background:var(--paper);color:var(--ink);font:400 17px/1.65 var(--sans);overflow-x:hidden}
img{max-width:100%;display:block;border:0}
a{color:inherit;text-decoration:none}
p{margin:0 0 1rem}
h1,h2,h3{font-family:var(--mono);font-weight:600;line-height:1.16;letter-spacing:-.015em;margin:0 0 .8rem}
h1{font-size:clamp(1.85rem,6.2vw,3.4rem)}
h2{font-size:clamp(1.25rem,3.2vw,1.7rem)}
h3{font-size:1.05rem}
hr{border:0;border-top:1px solid var(--ink);margin:1rem 0 1.3rem}
:focus-visible{outline:2px solid var(--ink);outline-offset:3px}

/* 顶栏 */
.top{position:sticky;top:0;z-index:30;background:var(--paper);border-bottom:1px solid var(--ink)}
.strip{padding:.45rem var(--pad);border-bottom:1px solid var(--ink);font-family:var(--mono);font-size:.8rem;letter-spacing:.2em;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
.bar{display:flex;align-items:center;justify-content:space-between;gap:1rem;padding:.55rem var(--pad)}
.mark{width:44px;height:44px;flex:0 0 44px;display:grid;place-items:center;background:var(--ink);color:var(--paper);border:1px solid var(--ink);font-family:var(--mono);font-weight:600;font-size:1.05rem;line-height:1;transition:background .22s ease,color .22s ease}
.mark img{width:100%;height:100%;object-fit:cover}
.mark:hover{background:var(--paper);color:var(--ink)}

/* 折叠菜单 */
.menu{position:relative;margin-left:auto}
.menu summary{list-style:none;cursor:pointer;display:flex;align-items:center;gap:.6rem;min-height:44px;padding:.5rem .85rem;border:1px solid var(--ink);font-family:var(--mono);font-size:.9rem;letter-spacing:.16em;transition:background .22s ease,color .22s ease}
.menu summary::-webkit-details-marker{display:none}
.menu summary::before{content:"";width:14px;height:10px;background:linear-gradient(var(--ink) 0 2px,transparent 2px 4px,var(--ink) 4px 6px,transparent 6px 8px,var(--ink) 8px 10px)}
.menu[open] summary{background:var(--ink);color:var(--paper)}
.menu[open] summary::before{background:linear-gradient(var(--paper) 0 2px,transparent 2px 4px,var(--paper) 4px 6px,transparent 6px 8px,var(--paper) 8px 10px)}
.menu menu{position:absolute;right:0;top:calc(100% + .5rem);width:min(19rem,calc(100vw - 2rem));margin:0;padding:.3rem;list-style:none;background:var(--paper);border:1px solid var(--ink)}
.menu menu a{display:flex;align-items:center;gap:.7rem;min-height:44px;padding:.4rem .7rem;font-size:1rem;border-bottom:1px solid var(--hair);transition:background .22s ease,color .22s ease}
.menu menu li:last-child a{border-bottom:0}
.menu menu a::before{content:"";width:8px;height:8px;flex:0 0 8px;background:var(--ink);transition:background .22s ease}
.menu menu a:hover,.menu menu a:focus-visible{background:var(--ink);color:var(--paper)}
.menu menu a:hover::before{background:var(--paper)}
@keyframes drop{from{opacity:0;transform:translateY(-6px)}to{opacity:1;transform:none}}
.menu[open] menu li{animation:drop .22s both}
.menu[open] menu li:nth-child(2){animation-delay:.03s}
.menu[open] menu li:nth-child(3){animation-delay:.06s}
.menu[open] menu li:nth-child(4){animation-delay:.09s}
.menu[open] menu li:nth-child(5){animation-delay:.12s}
.menu[open] menu li:nth-child(6){animation-delay:.15s}
.menu[open] menu li:nth-child(7){animation-delay:.18s}

/* 骨架 */
.shell{max-width:1200px;margin:0 auto;padding:0 var(--pad)}
.hero{display:grid;gap:1.4rem;align-content:start;min-height:45vh;padding:2.25rem 0 0}
.hero h1{margin:0}
.lead{max-width:54ch;margin:0;color:var(--muted);font-size:1.05rem}
.hero-fig{margin:0;aspect-ratio:16/6;border:1px solid var(--ink);border-radius:var(--r);overflow:hidden;background:var(--paper)}
.hero-fig img{width:100%;height:100%;object-fit:cover}
.hero-band{background:repeating-linear-gradient(112deg,var(--ink) 0 20px,var(--paper) 20px 40px)}
.slash{height:clamp(1.4rem,5vw,2.75rem);margin:2.25rem calc(-1 * var(--pad)) 0;background:var(--ink);transform:skewY(-1.6deg);transform-origin:left top}

/* 左侧目录 + 正文 */
.body{display:grid;grid-template-columns:minmax(0,17rem) minmax(0,1fr);gap:clamp(1.5rem,4vw,3rem);padding:2.5rem 0 3.5rem}
.side{align-self:start;padding:1.2rem 1.1rem;border:1px solid var(--ink);border-radius:var(--r)}
.side h2{margin:0;font-size:.85rem;letter-spacing:.22em}
.side hr{margin:.7rem 0 1rem}
.side ul{list-style:none;margin:0;padding:0;display:grid;gap:.1rem}
.side a{display:flex;align-items:center;gap:.65rem;min-height:40px;padding:.2rem 0;font-size:1rem;border-bottom:1px solid var(--hair)}
.side li:last-child a{border-bottom:0}
.side a::before{content:"";width:10px;height:1px;flex:0 0 10px;background:var(--ink);transition:width .22s ease}
.side a:hover::before{width:22px}

.prose{min-width:0}
.prose div{margin:0 0 1.4rem;padding:clamp(1.2rem,3vw,2rem);border:1px solid var(--ink);border-radius:var(--r);background:var(--paper);scroll-margin-top:8rem}
.prose div:last-child{margin-bottom:0}
.prose div > :first-child{margin-top:0}
.prose div > :last-child{margin-bottom:0}
.prose h2 + hr,.prose h3 + hr{margin-top:.6rem}
.prose p,.prose li{font-size:1.0625rem}
.prose ul,.prose ol{padding-left:1.15rem}
.prose li{margin:.2rem 0}
.prose a{border-bottom:1px solid var(--ink)}
.prose blockquote{margin:1.2rem 0;padding:.15rem 0 .15rem 1rem;border-left:3px solid var(--ink);font-family:var(--mono);font-size:.95rem}
.prose figure{margin:1.2rem 0;border:1px solid var(--ink);border-radius:12px;overflow:hidden}
.prose figcaption{padding:.5rem .8rem;border-top:1px solid var(--hair);font-size:.9rem;color:var(--muted)}
.prose img{width:100%;height:auto}
.prose table{width:100%;border-collapse:collapse;font-size:.98rem}
.prose th,.prose td{border:1px solid var(--hair);padding:.5rem .6rem;text-align:left}
.prose code,.prose pre{font-family:var(--mono);font-size:.95rem}
.prose pre{overflow-x:auto;padding:.9rem;border:1px solid var(--ink)}

/* 页脚 */
.foot{display:grid;grid-template-columns:1fr auto auto;gap:.6rem 2rem;align-items:center;border-top:1px solid var(--ink);padding:2rem max(var(--pad),calc((100vw - 1200px) / 2)) 2.25rem}
.foot p{margin:0}
.f-brand{font-family:var(--mono);font-weight:600}
.f-links{display:flex;flex-wrap:wrap;gap:0 .9rem;justify-content:center}
.f-links a{display:inline-flex;align-items:center;min-height:40px;font-size:1rem;border-bottom:1px solid transparent;transition:border-color .22s ease}
.f-links a:hover{border-color:var(--ink)}
.f-copy{text-align:right}
.f-copy small{font-family:var(--mono);font-size:.95rem;letter-spacing:.04em}

/* 入场 */
.js .reveal{opacity:0;transform:translateY(16px);transition:opacity .5s ease,transform .5s ease}
.js .reveal.in{opacity:1;transform:none}

@media (min-width:881px){
  .side{position:sticky;top:7.5rem}
}
@media (max-width:880px){
  .body{grid-template-columns:1fr}
  .hero{min-height:0}
  .foot{grid-template-columns:1fr;gap:.3rem}
  .f-links{justify-content:flex-start}
  .f-copy{text-align:left}
  .prose div{scroll-margin-top:7rem}
}
@media (max-width:420px){
  .hero-fig{aspect-ratio:16/8}
  .prose div{border-radius:14px}
}
@media (prefers-reduced-motion:reduce){
  html{scroll-behavior:auto}
  .js .reveal{opacity:1;transform:none;transition:none}
  .menu[open] menu li{animation:none}
}

button[aria-expanded]{min-width:44px;min-height:44px}