@import url('https://fonts.googleapis.com/css2?family=Nunito+Sans:wght@300;400;500;600;700&family=Rubik:wght@300;400;500;600;700&display=swap');

:root{
  --ink:#000000;
  --paper:#ffffff;
  --mute:#5b5b5b;
  --line:#000000;
  --hair:#d8d8d8;
  --wash:#f2f2f2;
  --ui:'Nunito Sans',system-ui,-apple-system,'Segoe UI','Microsoft YaHei',sans-serif;
  --display:'Rubik',var(--ui);
  --rail:224px;
  --pad:clamp(20px,5vw,56px);
}

*,*::before,*::after{box-sizing:border-box}

html{
  scroll-behavior:smooth;
  -webkit-text-size-adjust:100%;
}

body{
  margin:0;
  background:var(--paper);
  color:var(--ink);
  font-family:var(--ui);
  font-size:17px;
  line-height:1.7;
  overflow-x:hidden;
}

img{display:block;max-width:100%;height:auto}
a{color:inherit}
h1,h2,h3,h4{font-family:var(--display);font-weight:700}

/* ---------- 顶栏 ---------- */
.masthead{
  position:sticky;
  top:0;
  z-index:40;
  display:flex;
  align-items:center;
  flex-wrap:wrap;
  gap:10px 14px;
  padding:10px var(--pad);
  background:var(--paper);
  border-bottom:2px solid var(--line);
}

.mark{
  flex:0 0 auto;
  display:inline-flex;
  align-items:center;
  justify-content:center;
  width:40px;
  height:40px;
  border-radius:10px;
  background:var(--ink);
  color:var(--paper);
  font-family:var(--display);
  font-weight:700;
  font-size:20px;
  line-height:1;
  text-decoration:none;
}

.topnav{flex:1 1 260px;min-width:0}

.topnav ol{
  display:flex;
  flex-wrap:wrap;
  gap:8px;
  margin:0;
  padding:0;
  list-style:none;
}

.topnav a{
  display:inline-flex;
  align-items:center;
  min-height:40px;
  padding:0 14px;
  border:1.5px solid var(--line);
  border-radius:999px;
  font-size:16px;
  font-weight:600;
  line-height:1.2;
  text-decoration:none;
  transition:background .18s ease,color .18s ease;
}

.topnav a:hover,
.topnav a:focus-visible{
  background:var(--ink);
  color:var(--paper);
}

.cta{
  flex:0 0 auto;
  display:inline-flex;
  align-items:center;
  min-height:40px;
  padding:0 20px;
  border-radius:999px;
  background:var(--ink);
  color:var(--paper);
  font-size:16px;
  font-weight:700;
  text-decoration:none;
  border:1.5px solid var(--ink);
  transition:background .18s ease,color .18s ease;
}

.cta:hover,
.cta:focus-visible{
  background:var(--paper);
  color:var(--ink);
}

/* ---------- 首屏 ---------- */
.hero{
  min-height:100svh;
  display:grid;
  grid-template-rows:auto 1fr;
  gap:clamp(20px,4vw,40px);
  padding:clamp(28px,7vw,72px) var(--pad) 0;
  border-bottom:2px solid var(--line);
}

.hero-text{
  display:grid;
  justify-items:end;
  gap:16px;
  max-width:64ch;
  margin-left:auto;
  text-align:right;
}

.hero h1{
  margin:0;
  font-size:clamp(2.4rem,7.4vw,5.6rem);
  line-height:1.02;
  letter-spacing:-.025em;
  overflow-wrap:break-word;
}

.hero-lead{
  margin:0;
  max-width:44ch;
  color:var(--mute);
  font-size:clamp(16px,2vw,19px);
  line-height:1.6;
}

.hero-fig{
  margin:0;
  overflow:hidden;
  border-top:2px solid var(--line);
}

.hero-fig .hero-img{
  width:100%;
  height:100%;
  max-height:54svh;
  object-fit:cover;
  filter:grayscale(1) contrast(1.06);
  will-change:transform;
}

/* ---------- 主体骨架 ---------- */
main{display:block}

main div[id]{scroll-margin-top:96px}

.wrap{
  display:grid;
  grid-template-columns:var(--rail) minmax(0,1fr);
  gap:clamp(24px,4vw,60px);
  max-width:1180px;
  margin:0 auto;
  padding:clamp(28px,5vw,64px) var(--pad);
}

/* ---------- 左侧栏 ---------- */
.rail{
  align-self:start;
  position:sticky;
  top:92px;
  border-top:2px solid var(--line);
  padding-top:14px;
}

.rail-title{
  margin:0 0 4px;
  font-size:1.35rem;
  letter-spacing:.02em;
  line-height:1.2;
}

.subtitle{
  margin:0 0 14px;
  color:var(--mute);
  font-size:16px;
  line-height:1.5;
}

.railnav ol{
  margin:0;
  padding:0;
  list-style:none;
  counter-reset:rail;
}

.railnav li{counter-increment:rail}

.railnav a{
  display:flex;
  align-items:center;
  gap:8px;
  min-height:40px;
  padding:8px 0;
  border-bottom:1px solid var(--hair);
  font-size:16px;
  line-height:1.35;
  text-decoration:none;
}

.railnav a::before{
  content:counter(rail,decimal-leading-zero);
  font-family:var(--display);
  font-size:13px;
  font-weight:500;
  color:var(--mute);
  flex:0 0 auto;
}

.railnav a:hover{text-decoration:underline}

.rail-top{
  display:inline-flex;
  align-items:center;
  min-height:40px;
  margin-top:14px;
  font-size:16px;
  text-decoration:none;
  border-bottom:2px solid var(--line);
}

/* ---------- 正文 ---------- */
.body-sec{min-width:0}

.prose{
  max-width:72ch;
  font-size:17.5px;
  line-height:1.78;
}

.prose div{
  padding-top:clamp(26px,4vw,46px);
  margin-top:clamp(26px,4vw,46px);
  border-top:2px solid var(--line);
}

.prose div:first-of-type{
  margin-top:0;
  padding-top:0;
  border-top:0;
}

.prose h2{
  margin:0 0 16px;
  font-size:clamp(1.6rem,3.4vw,2.4rem);
  line-height:1.14;
  letter-spacing:-.015em;
}

.prose h3{
  margin:30px 0 10px;
  font-size:1.24rem;
  line-height:1.3;
}

.prose p{margin:0 0 18px}
.prose p:last-child{margin-bottom:0}

.prose div:first-of-type > p:first-of-type::first-letter{
  float:left;
  font-family:var(--display);
  font-size:4.1em;
  font-weight:700;
  line-height:.82;
  padding:.04em .1em 0 0;
}

.prose blockquote{
  margin:30px 0;
  padding:6px 0 6px 22px;
  border-left:8px solid var(--line);
  font-family:var(--display);
  font-size:clamp(1.15rem,2.4vw,1.6rem);
  font-weight:500;
  line-height:1.4;
}

.prose blockquote p{margin:0 0 8px}

.prose ul,
.prose ol{
  margin:0 0 18px;
  padding-left:1.25em;
}

.prose li{margin:0 0 8px}

.prose a{
  text-decoration:none;
  border-bottom:2px solid var(--line);
}

.prose a:hover{background:var(--ink);color:var(--paper)}

.prose strong{font-weight:700}

.prose hr{
  border:0;
  border-top:2px solid var(--line);
  margin:32px 0;
}

.prose figure{margin:26px 0}
.prose figcaption{
  font-size:16px;
  color:var(--mute);
  border-top:1px solid var(--hair);
  padding-top:8px;
  margin-top:8px;
}

.prose img{filter:grayscale(1)}
.prose img{width:100%}

.prose table{
  width:100%;
  border-collapse:collapse;
  margin:0 0 18px;
  font-size:16px;
}

.prose th,
.prose td{
  border:1px solid var(--line);
  padding:8px 10px;
  text-align:left;
}

/* ---------- 页脚 ---------- */
.foot{
  border-top:2px solid var(--line);
  padding:16px var(--pad);
}

.foot-bar{
  display:flex;
  align-items:center;
  justify-content:space-between;
  flex-wrap:wrap;
  gap:10px 20px;
  max-width:1180px;
  margin:0 auto;
}

.mark--flat{cursor:default}

.foot nav{flex:1 1 auto}

.foot nav ol{
  display:flex;
  flex-wrap:wrap;
  gap:4px 14px;
  margin:0;
  padding:0;
  list-style:none;
}

.foot nav a{
  display:inline-flex;
  align-items:center;
  min-height:40px;
  font-size:16px;
  text-decoration:none;
  border-bottom:1px solid transparent;
}

.foot nav a:hover{border-bottom-color:var(--line)}

.copy{
  margin:0;
  font-size:16px;
  color:var(--mute);
  white-space:nowrap;
}

/* ---------- 动效 ---------- */
body.reveal-on .reveal{
  opacity:0;
  transform:translateY(14px);
  transition:opacity .62s ease,transform .62s ease;
}

body.reveal-on .reveal.in{
  opacity:1;
  transform:none;
}

/* ---------- 断点 ---------- */
@media (max-width:900px){
  .wrap{grid-template-columns:1fr}
  .rail{position:static;top:auto}
  .railnav ol{display:flex;flex-wrap:wrap;gap:8px}
  .railnav li a::before{content:none}
  .railnav a{
    padding:0 12px;
    border:1px solid var(--line);
    border-radius:999px;
    font-size:16px;
  }
  .rail-top{margin-top:10px}
}

@media (max-width:640px){
  body{font-size:16.5px}
  .masthead{padding:8px 16px}
  .topnav{flex:1 1 100%;order:3}
  .topnav ol{gap:6px}
  .topnav a{padding:0 12px;font-size:16px}
  .hero{padding-top:24px}
  .hero-text{justify-items:end}
  .hero-fig .hero-img{max-height:40svh}
  .prose{font-size:17px}
  .foot nav{gap:2px 12px}
}

@media (prefers-reduced-motion:reduce){
  html{scroll-behavior:auto}
  body.reveal-on .reveal{opacity:1;transform:none;transition:none}
  .hero-fig .hero-img{transform:none!important}
}

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