*,*::before,*::after{box-sizing:border-box}
html{-webkit-text-size-adjust:100%;scroll-behavior:smooth;scroll-padding-top:96px}
body{margin:0}
h1,h2,h3,h4,h5,h6,p,ul,ol,figure,blockquote,dl,dd{margin:0}
ul,ol{padding:0;list-style:none}
img,svg,video{display:block;max-width:100%;height:auto}
button{font:inherit;color:inherit;background:none;border:0;padding:0;cursor:pointer}
a{color:inherit;text-decoration:none}
main{display:block}

:root{
  --ink-900:#07253B;
  --ink-700:#0E4A6B;
  --nacre:#F7F4EE;
  --nacre-2:#E4E0D6;
  --coral:#FF6A3D;
  --cyan:#2BE3C4;
  --text:#1B2A33;
  --coral-mist:#FFE3D8;
  --cyan-mist:#D6FBF3;
  --font-head:"PingFang SC","Hiragino Sans GB","Microsoft YaHei","Source Han Sans SC",system-ui,-apple-system,"Segoe UI",sans-serif;
  --font-body:"Songti SC","Noto Serif SC",Georgia,"Times New Roman","SimSun",serif;
  --font-mono:ui-monospace,SFMono-Regular,"SF Mono",Menlo,Consolas,"Courier New",monospace;
  --f-12:0.75rem;
  --f-16:1rem;
  --f-20:1.25rem;
  --f-28:1.75rem;
  --f-36:2rem;
  --f-56:clamp(2.25rem,4.6vw,3.5rem);
  --f-88:clamp(2.75rem,7.2vw,5.5rem);
  --shell:1180px;
  --gutter:clamp(1.25rem,4vw,3rem);
  --radius:26px;
  --radius-sm:16px;
  --pill:999px;
  --hairline:1px solid var(--nacre-2);
  --ease:cubic-bezier(.22,.61,.36,1);
}

body{
  background:var(--nacre);
  color:var(--text);
  font-family:var(--font-head);
  font-size:var(--f-16);
  line-height:1.75;
  -webkit-font-smoothing:antialiased;
  text-rendering:optimizeLegibility;
}
h1,h2,h3,h4,h5,h6{
  font-family:var(--font-head);
  font-weight:800;
  line-height:1.2;
  letter-spacing:-0.01em;
  color:var(--ink-900);
}
strong{font-weight:800}

.shell{
  width:100%;
  max-width:var(--shell);
  margin-inline:auto;
  padding-inline:var(--gutter);
}
.mono{
  font-family:var(--font-mono);
  font-variant-numeric:tabular-nums;
  letter-spacing:0.02em;
}
.visually-hidden{
  position:absolute;width:1px;height:1px;margin:-1px;padding:0;
  overflow:hidden;clip:rect(0 0 0 0);white-space:nowrap;border:0;
}
.skip-link{
  position:fixed;top:0;left:50%;z-index:999;
  transform:translate(-50%,-130%);
  padding:0.7rem 1.3rem;
  border-radius:0 0 var(--pill) var(--pill);
  background:var(--ink-900);color:var(--nacre);
  font-size:var(--f-12);font-weight:800;letter-spacing:0.12em;
  transition:transform 0.2s var(--ease);
}
.skip-link:focus{transform:translate(-50%,0)}
:where(a,button):focus-visible{
  outline:3px solid var(--ink-700);
  outline-offset:3px;
}
.site-footer :where(a,button):focus-visible{outline-color:var(--cyan)}

/* ---------- header ---------- */
.site-header{
  position:sticky;top:0;z-index:100;
  background:var(--nacre);
  border-bottom:1px solid var(--nacre-2);
}
.read-progress{
  display:block;height:2px;width:100%;
  background:var(--nacre-2);overflow:hidden;
}
.read-progress__bar{
  display:block;height:100%;width:0;
  background:linear-gradient(90deg,var(--coral) 0%,var(--cyan) 100%);
  transition:width 0.1s linear;
}
.masthead{position:relative}
.masthead__grid{
  display:grid;
  grid-template-columns:1fr auto 1fr;
  align-items:center;
  gap:0.75rem 1rem;
  padding-block:clamp(0.9rem,2vw,1.3rem) clamp(0.55rem,1.2vw,0.8rem);
  transition:padding-block 0.24s var(--ease);
}
.site-header[data-scrolled] .masthead__grid{
  padding-block:0.55rem 0.4rem;
}
.masthead__meta{
  justify-self:start;
  display:inline-flex;align-items:center;gap:0.45rem;
  font-family:var(--font-mono);
  font-size:var(--f-12);
  letter-spacing:0.1em;
  color:var(--ink-700);
}
.masthead__meta .mono{color:var(--ink-900);font-weight:700}
.brand{
  justify-self:center;
  display:flex;flex-direction:column;align-items:center;gap:0.2rem;
  padding:0.1rem 0.6rem;
}
.brand__cn{
  font-size:clamp(1.5rem,3.2vw,2rem);
  font-weight:900;
  letter-spacing:0.2em;
  line-height:1;
  color:var(--ink-900);
  transition:color 0.2s var(--ease);
}
.brand__en{
  font-family:var(--font-mono);
  font-size:var(--f-12);
  letter-spacing:0.34em;
  color:var(--ink-700);
}
.brand:hover .brand__cn{color:var(--coral)}
.masthead__aside{
  justify-self:end;
  display:flex;align-items:center;gap:0.55rem;
  flex-wrap:wrap;justify-content:flex-end;
}
.masthead__updated{
  display:inline-flex;align-items:center;gap:0.45rem;
  font-family:var(--font-mono);
  font-size:var(--f-12);
  letter-spacing:0.04em;
  color:var(--ink-700);
}
.dot{
  position:relative;flex:0 0 auto;
  width:8px;height:8px;border-radius:50%;
  background:var(--cyan);
}
.dot::after{
  content:"";position:absolute;inset:-3px;
  border:1px solid var(--cyan);border-radius:50%;opacity:0.5;
}

/* ---------- buttons ---------- */
.btn{
  display:inline-flex;align-items:center;justify-content:center;gap:0.45rem;
  padding:0.68rem 1.15rem;
  border:1px solid transparent;
  border-radius:var(--pill);
  font-family:var(--font-head);
  font-size:var(--f-12);
  font-weight:800;
  letter-spacing:0.08em;
  line-height:1;
  white-space:nowrap;
  transition:background-color 0.22s var(--ease),color 0.22s var(--ease),border-color 0.22s var(--ease);
}
.btn--coral{background:var(--coral);color:var(--ink-900)}
.btn--coral:hover{background:#FF8158}
.btn--cyan{background:var(--cyan);color:var(--ink-900)}
.btn--cyan:hover{background:#5EEBD4}
.btn--outline{border-color:var(--ink-900);color:var(--ink-900)}
.btn--outline:hover{background:var(--ink-900);color:var(--nacre)}
.btn--outline-light{border-color:rgba(247,244,238,0.45);color:var(--nacre)}
.btn--outline-light:hover{background:var(--nacre);color:var(--ink-900);border-color:var(--nacre)}
.btn-row{display:flex;flex-wrap:wrap;gap:0.6rem;align-items:center}

/* ---------- navigation ---------- */
.nav{position:relative}
.nav__inner{
  display:flex;align-items:center;justify-content:center;gap:0.5rem;
  padding-block:0.25rem 0.6rem;
}
.nav__toggle{display:none}
.nav__list{
  display:flex;align-items:center;justify-content:center;
  flex-wrap:wrap;
  gap:clamp(0.3rem,1.8vw,1.4rem);
}
.nav__item{display:block}
.nav__link{
  position:relative;
  display:inline-flex;align-items:baseline;gap:0.32rem;
  padding:0.4rem 0.6rem;
  border-radius:var(--pill);
  font-size:var(--f-16);
  font-weight:700;
  letter-spacing:0.02em;
  color:var(--ink-700);
  transition:color 0.2s var(--ease),background-color 0.2s var(--ease);
}
.nav__link::after{
  content:"";position:absolute;left:50%;bottom:0.12rem;
  height:3px;width:0;border-radius:3px;
  background:var(--coral);
  transform:translateX(-50%);
  transition:width 0.24s var(--ease);
}
.nav__link:hover{color:var(--ink-900)}
.nav__link:hover::after{width:calc(100% - 1.2rem)}
.nav__link[aria-current="page"]{
  color:var(--ink-900);
  background:var(--coral-mist);
}
.nav__link[aria-current="page"]::after{width:calc(100% - 1.2rem)}
.nav__num{
  font-family:var(--font-mono);
  font-size:var(--f-12);
  font-weight:400;
  letter-spacing:0.02em;
  font-variant-numeric:tabular-nums;
  color:var(--ink-700);
  opacity:0.6;
}
.nav__link[aria-current="page"] .nav__num{color:var(--coral);opacity:1}

/* ---------- version band ---------- */
.version-band{background:var(--ink-900);color:var(--nacre)}
.version-band__inner{
  display:flex;flex-wrap:wrap;align-items:center;
  gap:0.3rem 0.85rem;
  padding-block:0.5rem;
  font-family:var(--font-mono);
  font-size:var(--f-12);
  letter-spacing:0.06em;
  line-height:1.5;
}
.version-band__item{display:inline-flex;align-items:center;gap:0.45rem}
.version-band__item--cyan{color:var(--cyan)}
.version-band__sep{
  width:1px;height:11px;flex:0 0 auto;
  background:rgba(247,244,238,0.28);
}
.version-band__link{
  color:var(--nacre);
  border-bottom:1px solid rgba(247,244,238,0.45);
  padding-bottom:1px;
  transition:color 0.2s var(--ease),border-color 0.2s var(--ease);
}
.version-band__link:hover{color:var(--cyan);border-color:var(--cyan)}

/* ---------- footer ---------- */
.site-footer{
  position:relative;
  overflow:hidden;
  background:var(--ink-900);
  color:var(--nacre);
  padding-block:clamp(2.5rem,5vw,4rem) 1.5rem;
}
.site-footer::before{
  content:"";
  position:absolute;inset:auto 0 -30% 0;
  height:70%;
  pointer-events:none;
  opacity:0.55;
  background:repeating-radial-gradient(140% 120% at 50% 130%,rgba(43,227,196,0.13) 0 1px,transparent 1px 28px);
}
.footer__grid{
  position:relative;
  display:grid;
  grid-template-columns:1.2fr 1.05fr 0.85fr 1fr;
  gap:clamp(1.5rem,3vw,2.75rem);
}
.footer__col{
  min-width:0;
  padding-top:1rem;
  border-top:1px solid rgba(247,244,238,0.2);
}
.footer__index{
  font-family:var(--font-mono);
  font-size:var(--f-12);
  letter-spacing:0.2em;
  color:var(--cyan);
}
.footer__wordmark{
  margin-top:0.5rem;
  font-size:var(--f-36);
  font-weight:900;
  letter-spacing:0.22em;
  line-height:1.1;
  color:var(--nacre);
}
.footer__tagline{
  margin-top:0.35rem;
  font-size:var(--f-12);
  letter-spacing:0.06em;
  color:rgba(247,244,238,0.6);
}
.footer__title{
  margin-top:0.5rem;
  font-size:var(--f-20);
  font-weight:800;
  letter-spacing:0.04em;
  color:var(--nacre);
}
.footer__list{
  margin-top:0.9rem;
  display:grid;
  gap:0.55rem;
}
.footer__link{
  display:inline-flex;align-items:baseline;gap:0.45rem;
  font-size:var(--f-16);
  line-height:1.5;
  color:rgba(247,244,238,0.78);
  transition:color 0.2s var(--ease);
}
.footer__link:hover{color:var(--nacre);text-decoration:underline;text-underline-offset:4px;text-decoration-color:var(--cyan)}
.footer__link--download{
  position:relative;
  padding-left:1.1rem;
  color:var(--nacre);
}
.footer__link--download::before{
  content:"↓";
  position:absolute;left:0;top:0;
  font-family:var(--font-mono);
  color:var(--coral);
}
.footer__link--download:hover::before{color:var(--cyan)}
.footer__num{
  font-family:var(--font-mono);
  font-size:var(--f-12);
  color:rgba(247,244,238,0.45);
  font-variant-numeric:tabular-nums;
}
.footer__text{
  font-size:var(--f-16);
  line-height:1.6;
  color:rgba(247,244,238,0.78);
  word-break:break-word;
}
.footer__cta{margin-top:1.1rem}
.footer__note{
  position:relative;
  margin-top:clamp(1.75rem,4vw,2.75rem);
  max-width:60ch;
  font-size:var(--f-12);
  line-height:1.8;
  color:rgba(247,244,238,0.5);
}
.footer__legal{
  position:relative;
  margin-top:1.25rem;
  padding-top:1.1rem;
  border-top:1px solid rgba(247,244,238,0.18);
  display:flex;flex-wrap:wrap;align-items:center;justify-content:space-between;
  gap:0.6rem 1.5rem;
  font-size:var(--f-12);
  color:rgba(247,244,238,0.6);
}
.footer__copy{
  font-family:var(--font-mono);
  letter-spacing:0.06em;
}
.footer__legal-links{display:flex;flex-wrap:wrap;gap:0.6rem 1.25rem}
.footer__legal-links a{transition:color 0.2s var(--ease)}
.footer__legal-links a:hover{color:var(--cyan)}

/* ---------- sections ---------- */
.section{padding-block:clamp(2.75rem,6vw,5.5rem)}
.section--tight{padding-block:clamp(2rem,4vw,3rem)}
.section--mist{background:var(--nacre-2)}
.section--dark{background:var(--ink-900);color:var(--nacre)}
.section--dark .section__title,
.section--dark h2,
.section--dark h3{color:var(--nacre)}
.section--dark .eyebrow{color:var(--cyan)}
.section--dark .section__num{color:rgba(247,244,238,0.28)}
.section__head{
  display:flex;flex-wrap:wrap;align-items:baseline;
  gap:0.5rem 1.15rem;
  margin-bottom:clamp(1.25rem,3vw,2.25rem);
}
.section__num{
  font-family:var(--font-mono);
  font-size:var(--f-56);
  font-weight:700;
  line-height:0.9;
  letter-spacing:-0.02em;
  font-variant-numeric:tabular-nums;
  color:var(--nacre-2);
  transition:color 0.24s var(--ease),transform 0.24s var(--ease);
}
.section__num.is-active{color:var(--coral)}
.section__title{
  font-size:clamp(1.5rem,3vw,2.25rem);
  font-weight:900;
  line-height:1.25;
  color:var(--ink-900);
}
.display{
  font-size:var(--f-88);
  font-weight:900;
  line-height:1.02;
  letter-spacing:-0.03em;
  color:var(--ink-900);
}
.eyebrow{
  display:inline-flex;align-items:center;gap:0.5rem;
  font-family:var(--font-mono);
  font-size:var(--f-12);
  letter-spacing:0.24em;
  text-transform:uppercase;
  color:var(--ink-700);
}
.lede{
  font-family:var(--font-head);
  font-size:var(--f-20);
  line-height:1.7;
  font-weight:500;
  color:var(--ink-700);
  max-width:32em;
}
.prose{
  font-family:var(--font-body);
  font-size:var(--f-16);
  line-height:1.85;
  color:var(--text);
  max-width:36em;
}
.prose p+p{margin-top:1em}
.prose h2,.prose h3{
  font-family:var(--font-head);
  margin-top:1.6em;margin-bottom:0.6em;
}
.prose ul,.prose ol{margin-top:0.8em;display:grid;gap:0.4em}
.prose li{position:relative;padding-left:1.15em}
.prose li::before{
  content:"";position:absolute;left:0;top:0.72em;
  width:6px;height:6px;border-radius:50%;background:var(--coral);
}
.big-num{
  font-family:var(--font-mono);
  font-size:var(--f-56);
  font-weight:700;
  line-height:1;
  letter-spacing:0.02em;
  font-variant-numeric:tabular-nums;
  color:var(--ink-900);
}
.divider{
  height:0;border:0;border-top:var(--hairline);
  margin-block:clamp(1.5rem,3vw,2.5rem);
}

/* ---------- grids ---------- */
.grid{display:grid;gap:clamp(1.25rem,3vw,2.5rem)}
.grid--2{grid-template-columns:repeat(2,minmax(0,1fr))}
.grid--3{grid-template-columns:repeat(3,minmax(0,1fr))}
.grid--main-aside{grid-template-columns:minmax(0,7fr) minmax(0,4fr)}
.grid--aside-main{grid-template-columns:minmax(0,3fr) minmax(0,8fr)}

/* ---------- crumbs ---------- */
.crumbs{margin-block:clamp(1rem,2.5vw,1.75rem)}
.crumbs__list{
  display:flex;flex-wrap:wrap;align-items:center;gap:0.5rem;
  font-family:var(--font-mono);
  font-size:var(--f-12);
  letter-spacing:0.06em;
  color:var(--ink-700);
}
.crumbs__item{display:inline-flex;align-items:center;gap:0.5rem}
.crumbs__link{color:var(--ink-700);transition:color 0.2s var(--ease)}
.crumbs__link:hover{color:var(--coral)}
.crumbs__sep{color:rgba(14,74,107,0.4)}
.crumbs__current{color:var(--ink-900);font-weight:700}

/* ---------- cards & tags ---------- */
.card{
  background:var(--nacre-2);
  border-radius:var(--radius);
  padding:clamp(1.1rem,2.4vw,1.9rem);
}
.card--paper{background:var(--nacre);border:var(--hairline)}
.card--dark{background:var(--ink-900);color:var(--nacre)}
.card__title{
  font-size:var(--f-20);
  font-weight:800;
  letter-spacing:0.01em;
  color:var(--ink-900);
}
.card--dark .card__title{color:var(--nacre)}
.card__meta{
  margin-top:0.4rem;
  font-family:var(--font-mono);
  font-size:var(--f-12);
  letter-spacing:0.08em;
  color:var(--ink-700);
}
.card--dark .card__meta{color:rgba(247,244,238,0.6)}
.tag{
  display:inline-flex;align-items:center;gap:0.45rem;
  padding:0.3rem 0.85rem;
  border-radius:var(--pill);
  font-size:var(--f-12);
  font-weight:800;
  letter-spacing:0.08em;
  line-height:1.4;
  background:var(--nacre-2);
  color:var(--ink-900);
}
.tag::before{
  content:"";width:7px;height:7px;border-radius:50%;
  background:var(--ink-700);flex:0 0 auto;
}
.tag--a{background:var(--coral-mist);color:var(--ink-900)}
.tag--a::before{background:var(--coral)}
.tag--b{background:var(--cyan-mist);color:var(--ink-900)}
.tag--b::before{background:var(--cyan)}
.tag--c{background:var(--nacre-2);color:var(--ink-900)}
.tag--c::before{background:var(--ink-700)}

/* ---------- media ---------- */
.media{
  position:relative;
  display:block;
  overflow:hidden;
  border-radius:var(--radius);
  background-color:var(--nacre-2);
  background-image:repeating-linear-gradient(115deg,rgba(14,74,107,0.1) 0 1px,transparent 1px 14px);
}
.media img,.media svg{width:100%;height:100%;object-fit:cover;display:block}
.media--169{aspect-ratio:16/9}
.media--43{aspect-ratio:4/3}
.media--11{aspect-ratio:1/1}
.media--wide{aspect-ratio:21/9}
.media__caption{
  margin-top:0.6rem;
  font-family:var(--font-mono);
  font-size:var(--f-12);
  letter-spacing:0.04em;
  color:var(--ink-700);
}

/* ---------- notice & checklist ---------- */
.notice{
  border-left:4px solid var(--coral);
  background:var(--coral-mist);
  color:var(--ink-900);
  border-radius:var(--radius-sm);
  padding:1rem 1.25rem;
  font-size:var(--f-16);
  line-height:1.7;
}
.notice--cyan{background:var(--cyan-mist);border-left-color:var(--cyan)}
.check-list{display:grid;gap:0.5rem}
.check-list__item{
  display:flex;align-items:flex-start;gap:0.7rem;
  padding:0.7rem 0.9rem;
  background:var(--nacre);
  border:var(--hairline);
  border-radius:var(--radius-sm);
  font-size:var(--f-16);
  line-height:1.6;
  transition:background-color 0.22s var(--ease),border-color 0.22s var(--ease);
}
.check-list__box{
  flex:0 0 auto;
  width:16px;height:16px;margin-top:0.28em;
  border:1.5px solid var(--ink-700);
  border-radius:5px;
  transition:background-color 0.22s var(--ease),border-color 0.22s var(--ease);
}
.check-list__num{
  font-family:var(--font-mono);
  font-size:var(--f-12);
  letter-spacing:0.04em;
  color:var(--ink-700);
}
.check-list__item[data-done]{
  background:var(--cyan-mist);
  border-color:var(--cyan);
}
.check-list__item[data-done] .check-list__box{
  background:var(--cyan);
  border-color:var(--cyan);
}

/* ---------- responsive ---------- */
@media (min-width:861px){
  html{scroll-padding-top:132px}
}
@media (max-width:1000px){
  .footer__grid{grid-template-columns:repeat(2,minmax(0,1fr))}
  .grid--main-aside,.grid--aside-main{grid-template-columns:minmax(0,1fr)}
}
@media (max-width:860px){
  .masthead__grid{
    grid-template-columns:1fr auto;
    grid-template-areas:"brand brand" "meta aside";
    row-gap:0.7rem;
    padding-block:0.85rem 0.6rem;
  }
  .brand{grid-area:brand;justify-self:center}
  .masthead__meta{grid-area:meta}
  .masthead__aside{grid-area:aside}
  .nav__inner{
    flex-direction:column;align-items:stretch;
    padding-block:0.35rem 0.6rem;
  }
  .nav__toggle{
    display:inline-flex;align-items:center;gap:0.55rem;
    align-self:flex-start;
    padding:0.55rem 1rem;
    border:1px solid var(--ink-900);
    border-radius:var(--pill);
    font-size:var(--f-12);
    font-weight:800;
    letter-spacing:0.12em;
    color:var(--ink-900);
    transition:color 0.2s var(--ease),border-color 0.2s var(--ease);
  }
  .nav__toggle-bars{position:relative;display:block;width:16px;height:10px}
  .nav__toggle-bars::before,
  .nav__toggle-bars::after{
    content:"";position:absolute;left:0;right:0;
    height:2px;border-radius:2px;background:currentColor;
    transition:transform 0.22s var(--ease),top 0.22s var(--ease),bottom 0.22s var(--ease);
  }
  .nav__toggle-bars::before{top:0}
  .nav__toggle-bars::after{bottom:0}
  [data-nav][data-open] .nav__toggle{border-color:var(--coral);color:var(--coral)}
  [data-nav][data-open] .nav__toggle-bars::before{top:4px;transform:rotate(45deg)}
  [data-nav][data-open] .nav__toggle-bars::after{bottom:4px;transform:rotate(-45deg)}
  .nav__list{
    display:none;
    width:100%;
    flex-direction:column;
    align-items:stretch;
    gap:0.3rem;
    margin-top:0.55rem;
    padding-top:0.55rem;
    border-top:1px solid var(--nacre-2);
  }
  [data-nav][data-open] .nav__list{display:flex}
  .nav__link{
    display:flex;
    justify-content:flex-start;
    padding:0.6rem 0.95rem;
    background:var(--nacre-2);
    border-radius:var(--pill);
  }
  .nav__link::after{display:none}
  .nav__link[aria-current="page"]{background:var(--coral-mist);color:var(--ink-900)}
  .grid--2,.grid--3{grid-template-columns:minmax(0,1fr)}
}
@media (max-width:620px){
  .masthead__updated{display:none}
  .masthead__aside .btn--outline{display:none}
  .footer__grid{grid-template-columns:minmax(0,1fr)}
  .version-band__sep{display:none}
  .version-band__inner{row-gap:0.2rem}
  .section__num{font-size:var(--f-36)}
}

/* ---------- motion & focus ---------- */
@media (prefers-reduced-motion:reduce){
  html{scroll-behavior:auto}
  *,*::before,*::after{
    animation-duration:0.001ms !important;
    animation-iteration-count:1 !important;
    transition-duration:0.001ms !important;
    transition-delay:0ms !important;
    scroll-behavior:auto !important;
  }
}