:root{
  --yf-night:#0B1220;
  --yf-panel:#111C2E;
  --yf-line:#1E2C44;
  --yf-paper:#F4EFE6;
  --yf-mint:#6FE3C4;
  --yf-cinnabar:#FF6A3D;
  --yf-lime:#A6F25C;
  --yf-mist:#9AA7BA;
  --yf-ink:#1A1614;
  --yf-snow:#E8EDF5;

  --yf-sans:"PingFang SC","Hiragino Sans GB","Microsoft YaHei","Source Han Sans SC","Noto Sans SC",system-ui,-apple-system,"Segoe UI",Roboto,sans-serif;
  --yf-mono:ui-monospace,SFMono-Regular,"SF Mono",Menlo,Consolas,"Liberation Mono","Courier New",monospace;

  --yf-t14:0.875rem;
  --yf-t18:1.125rem;
  --yf-t22:1.375rem;
  --yf-t28:1.75rem;
  --yf-t36:2.25rem;
  --yf-t44:2.75rem;
  --yf-t64:4rem;
  --yf-t88:5.5rem;

  --yf-radius-s:12px;
  --yf-radius-m:18px;
  --yf-radius-l:26px;
  --yf-wrap:1320px;
  --yf-ease:cubic-bezier(.22,.61,.36,1);
  --yf-dur:180ms;
}

*,*::before,*::after{box-sizing:border-box;}
html{-webkit-text-size-adjust:100%;}
body{
  margin:0;
  font-family:var(--yf-sans);
  font-size:var(--yf-t18);
  line-height:1.85;
  color:var(--yf-snow);
  background:var(--yf-night);
  -webkit-font-smoothing:antialiased;
  -webkit-tap-highlight-color:transparent;
}
h1,h2,h3,h4,p,ul,ol,figure,blockquote{margin:0;}
ul,ol{padding:0;list-style:none;}
img,svg{max-width:100%;}
a{color:inherit;}
button{font:inherit;color:inherit;background:none;border:0;cursor:pointer;}
:where(a,button,[tabindex]):focus-visible{outline:2px solid var(--yf-mint);outline-offset:3px;border-radius:6px;}
#main-content:focus{outline:none;}

/* ---------- typography ---------- */
h1,h2,h3,h4{font-weight:800;letter-spacing:-0.02em;line-height:1.15;text-wrap:balance;}
h1{font-size:clamp(var(--yf-t44),6vw,var(--yf-t88));}
h2{font-size:clamp(var(--yf-t28),3.4vw,var(--yf-t44));}
h3{font-size:var(--yf-t22);}
h4{font-size:var(--yf-t18);}
p{text-wrap:pretty;}

.yf-mono{font-family:var(--yf-mono);letter-spacing:0.02em;}

.yf-eyebrow{
  display:inline-flex;align-items:center;gap:10px;
  font-family:var(--yf-mono);
  font-size:var(--yf-t14);
  letter-spacing:0.14em;
  color:var(--yf-mint);
}
.yf-eyebrow::before{content:"";width:24px;height:1px;background:currentColor;flex:none;}

/* ---------- layout utilities ---------- */
.yf-wrap{
  width:100%;max-width:var(--yf-wrap);
  margin:0 auto;padding:0 24px;
}
.yf-prose{max-width:68ch;}
.yf-prose p + p{margin-top:1.2em;}
.yf-grid{
  display:grid;
  grid-template-columns:repeat(12,minmax(0,1fr));
  gap:24px;
}
.yf-band{
  height:6px;border-radius:999px;
  background:linear-gradient(90deg,var(--yf-mint),var(--yf-lime) 55%,var(--yf-cinnabar));
}
.yf-divider{height:1px;border:0;background:var(--yf-line);margin:0;}

/* ---------- cards ---------- */
.yf-card{
  background:var(--yf-panel);
  border:1px solid var(--yf-line);
  border-radius:var(--yf-radius-l);
  padding:28px;
  transition:transform var(--yf-dur) var(--yf-ease),border-color var(--yf-dur) var(--yf-ease);
}
.yf-card:hover{transform:translateY(-2px);border-color:rgba(111,227,196,.45);}
.yf-card--paper{
  background:var(--yf-paper);
  color:var(--yf-ink);
  border-color:#DED6C6;
  font-size:var(--yf-t18);
}
.yf-card--paper a{color:#8A3A12;}

/* ---------- buttons ---------- */
.yf-btn{
  display:inline-flex;align-items:center;justify-content:center;gap:0.45em;
  font-family:var(--yf-sans);
  font-size:var(--yf-t14);
  font-weight:700;
  letter-spacing:0.02em;
  line-height:1;
  padding:11px 20px;
  border-radius:999px;
  border:1px solid transparent;
  text-decoration:none;
  white-space:nowrap;
  transition:transform var(--yf-dur) var(--yf-ease),background-color var(--yf-dur) var(--yf-ease),border-color var(--yf-dur) var(--yf-ease),color var(--yf-dur) var(--yf-ease);
}
.yf-btn--primary{background:var(--yf-cinnabar);color:#170B06;border-color:var(--yf-cinnabar);}
.yf-btn--primary:hover{background:#FF8158;border-color:#FF8158;transform:translateY(-1px);}
.yf-btn--ghost{background:transparent;color:var(--yf-mint);border-color:rgba(111,227,196,.38);}
.yf-btn--ghost:hover{color:var(--yf-night);background:var(--yf-mint);border-color:var(--yf-mint);transform:translateY(-1px);}
.yf-btn--paper{background:var(--yf-paper);color:var(--yf-ink);border-color:var(--yf-paper);}
.yf-btn--paper:hover{transform:translateY(-1px);}
.yf-btn--lime{background:var(--yf-lime);color:#12200A;border-color:var(--yf-lime);}
.yf-btn--lime:hover{transform:translateY(-1px);}

/* ---------- skip link ---------- */
.yf-skip{
  position:fixed;top:10px;left:10px;z-index:300;
  padding:12px 22px;
  border-radius:999px;
  background:var(--yf-mint);
  color:#062018;
  font-size:var(--yf-t14);
  font-weight:700;
  text-decoration:none;
  transform:translateY(-180%);
  transition:transform var(--yf-dur) var(--yf-ease);
}
.yf-skip:focus,
.yf-skip:focus-visible{transform:translateY(0);outline:2px solid var(--yf-night);outline-offset:2px;}

/* ---------- header ---------- */
.yf-header{
  --yf-hh:64px;
  position:sticky;top:0;z-index:100;
  background:rgba(11,18,32,0.92);
  -webkit-backdrop-filter:blur(12px);
  backdrop-filter:blur(12px);
  border-bottom:1px solid var(--yf-line);
  transition:background-color var(--yf-dur) var(--yf-ease);
}
.yf-header[data-scrolled]{
  --yf-hh:52px;
  background:rgba(11,18,32,0.975);
  border-bottom-color:#243454;
}
.yf-header::before{
  content:"";position:absolute;inset:0;pointer-events:none;
  background:
    radial-gradient(70% 200% at 0% 0%,rgba(111,227,196,.07),transparent 60%),
    radial-gradient(50% 180% at 100% 0%,rgba(255,106,61,.05),transparent 60%);
}
.yf-header__inner{
  position:relative;z-index:1;
  display:flex;align-items:center;gap:20px;
  width:100%;max-width:var(--yf-wrap);
  margin:0 auto;padding:0 24px;
  min-height:var(--yf-hh);
  transition:min-height var(--yf-dur) var(--yf-ease);
}

/* brand */
.yf-brand{
  display:inline-flex;align-items:center;gap:12px;
  text-decoration:none;color:var(--yf-snow);
  flex:none;
}
.yf-brand__mark{
  display:grid;place-items:center;
  width:36px;height:36px;flex:none;
  border-radius:var(--yf-radius-s);
  background:linear-gradient(150deg,rgba(111,227,196,.22),rgba(255,106,61,.18));
  border:1px solid rgba(111,227,196,.45);
  color:var(--yf-mint);
  font-weight:800;font-size:var(--yf-t18);line-height:1;
}
.yf-brand__text{display:flex;flex-direction:column;line-height:1.2;}
.yf-brand__name{font-size:var(--yf-t18);font-weight:800;letter-spacing:-0.01em;}
.yf-brand__sub{
  font-family:var(--yf-mono);
  font-size:var(--yf-t14);
  letter-spacing:0.02em;
  color:var(--yf-mist);
  margin-top:2px;
}
.yf-brand--footer .yf-brand__mark{width:42px;height:42px;font-size:var(--yf-t22);}

/* nav */
.yf-nav{margin-left:auto;}
.yf-nav__list{display:flex;align-items:center;gap:2px;}
.yf-nav__link{
  position:relative;
  display:block;
  padding:9px 12px;
  font-family:var(--yf-mono);
  font-size:var(--yf-t14);
  letter-spacing:0.02em;
  color:var(--yf-mist);
  text-decoration:none;
  border-radius:8px;
  white-space:nowrap;
  transition:color var(--yf-dur) var(--yf-ease);
}
.yf-nav__link::after{
  content:"";position:absolute;left:12px;right:12px;bottom:0;
  height:2px;border-radius:2px;
  background:var(--yf-lime);
  transform:scaleX(0);transform-origin:0 50%;
  transition:transform var(--yf-dur) var(--yf-ease);
}
.yf-nav__link:hover{color:var(--yf-snow);}
.yf-nav__link:hover::after{transform:scaleX(1);}
.yf-nav__link[aria-current="page"]{color:var(--yf-snow);}
.yf-nav__link[aria-current="page"]::after{transform:scaleX(1);}

/* header actions */
.yf-header__actions{display:flex;align-items:center;gap:10px;flex:none;}

/* toggle */
.yf-navtoggle{
  display:none;
  align-items:center;gap:8px;
  margin-left:auto;
  padding:10px 14px;
  border-radius:999px;
  border:1px solid var(--yf-line);
  background:rgba(17,28,46,.7);
  color:var(--yf-snow);
  font-family:var(--yf-mono);
  font-size:var(--yf-t14);
  order:3;
  flex:none;
}
.yf-navtoggle__icon{position:relative;display:block;width:18px;height:12px;flex:none;}
.yf-navtoggle__icon::before,
.yf-navtoggle__icon::after{
  content:"";position:absolute;left:0;right:0;height:2px;border-radius:2px;
  background:var(--yf-mint);
  transition:transform var(--yf-dur) var(--yf-ease),top var(--yf-dur) var(--yf-ease);
}
.yf-navtoggle__icon::before{top:1px;}
.yf-navtoggle__icon::after{top:9px;}
.yf-navtoggle__label::after{content:"菜单";}
.yf-header[data-open] .yf-navtoggle__icon::before{top:5px;transform:rotate(45deg);}
.yf-header[data-open] .yf-navtoggle__icon::after{top:5px;transform:rotate(-45deg);}
.yf-header[data-open] .yf-navtoggle__label::after{content:"关闭";}
.yf-header[data-open] .yf-navtoggle{border-color:rgba(111,227,196,.5);}

/* progress */
.yf-progress{
  position:absolute;left:0;right:0;bottom:-1px;
  height:3px;pointer-events:none;
  background:rgba(30,44,68,.5);
}
.yf-progress__bar{
  display:block;height:100%;width:100%;
  background:linear-gradient(90deg,var(--yf-mint),var(--yf-lime));
  transform:scaleX(0);transform-origin:0 50%;
}

/* ---------- footer ---------- */
.yf-footer{
  position:relative;
  margin-top:0;
  background-color:#080E19;
  background-image:
    radial-gradient(80% 130% at 100% 0%,rgba(111,227,196,.09),transparent 58%),
    radial-gradient(60% 110% at 0% 0%,rgba(255,106,61,.07),transparent 55%);
  border-top:1px solid var(--yf-line);
  color:var(--yf-snow);
  font-size:var(--yf-t14);
  line-height:1.75;
}
.yf-footer__inner{
  width:100%;max-width:var(--yf-wrap);
  margin:0 auto;padding:0 24px;
}
.yf-footer__belt{padding:56px 0 8px;}
.yf-footer__belt-title{
  font-size:var(--yf-t28);
  font-weight:800;
  letter-spacing:-0.02em;
  color:var(--yf-snow);
  margin:10px 0 24px;
}

.yf-belt{
  display:grid;
  grid-template-columns:1.4fr 1fr 1fr 1.2fr;
  gap:14px;
}
.yf-belt__item{
  position:relative;
  display:flex;flex-direction:column;
  padding:20px 22px 22px;
  border-radius:var(--yf-radius-m);
  background:var(--yf-panel);
  border:1px solid var(--yf-line);
  color:var(--yf-snow);
  text-decoration:none;
  transition:transform var(--yf-dur) var(--yf-ease),border-color var(--yf-dur) var(--yf-ease),background-color var(--yf-dur) var(--yf-ease);
}
.yf-belt__item:hover{transform:translateY(-2px);border-color:rgba(111,227,196,.55);}
.yf-belt__idx{
  font-family:var(--yf-mono);
  font-size:var(--yf-t14);
  color:var(--yf-mist);
  letter-spacing:0.08em;
}
.yf-belt__label{
  display:block;
  margin-top:16px;
  font-size:var(--yf-t22);
  font-weight:800;
  letter-spacing:-0.01em;
  line-height:1.3;
}
.yf-belt__cap{
  display:block;
  margin-top:6px;
  font-size:var(--yf-t14);
  line-height:1.6;
  color:var(--yf-mist);
}
.yf-belt__item--lead{
  background:linear-gradient(140deg,var(--yf-mint),#4CD0AE 70%,#3FC5A4);
  border-color:var(--yf-mint);
  color:#07211B;
}
.yf-belt__item--lead:hover{border-color:var(--yf-lime);}
.yf-belt__item--lead .yf-belt__idx{color:rgba(7,33,27,.62);}
.yf-belt__item--lead .yf-belt__cap{color:rgba(7,33,27,.74);}

.yf-footer__main{padding:56px 0 8px;}
.yf-footer__grid{
  display:grid;
  grid-template-columns:1.7fr repeat(3,minmax(0,1fr));
  gap:44px 32px;
}
.yf-footer__note{
  margin-top:18px;
  max-width:30ch;
  color:var(--yf-mist);
  font-size:var(--yf-t14);
  line-height:1.7;
}
.yf-contact{margin-top:24px;display:grid;gap:10px;}
.yf-contact__row{
  display:grid;
  grid-template-columns:44px minmax(0,1fr);
  gap:12px;
  font-size:var(--yf-t14);
  line-height:1.65;
}
.yf-contact__k{
  font-family:var(--yf-mono);
  color:var(--yf-mint);
  letter-spacing:0.08em;
}
.yf-contact__v{color:var(--yf-mist);word-break:break-word;}

.yf-col__title{
  font-family:var(--yf-mono);
  font-size:var(--yf-t14);
  letter-spacing:0.14em;
  color:var(--yf-mint);
  margin-bottom:16px;
}
.yf-col__list{display:grid;gap:10px;}
.yf-col__link{
  display:inline-block;
  font-size:var(--yf-t14);
  color:var(--yf-snow);
  text-decoration:none;
  border-bottom:1px solid transparent;
  transition:color var(--yf-dur) var(--yf-ease),border-color var(--yf-dur) var(--yf-ease);
}
.yf-col__link:hover{color:var(--yf-mint);border-bottom-color:currentColor;}

.yf-footer__legal{
  display:flex;flex-wrap:wrap;align-items:center;gap:12px 28px;
  margin-top:24px;padding:22px 0 40px;
  border-top:1px solid var(--yf-line);
  font-family:var(--yf-mono);
  font-size:var(--yf-t14);
  color:var(--yf-mist);
}
.yf-footer__copy{margin:0;}
.yf-footer__icp{
  margin:0;
  color:var(--yf-lime);
  letter-spacing:0.04em;
}
.yf-footer__legal-links{
  display:flex;flex-wrap:wrap;gap:18px;
  margin:0 0 0 auto;
}

/* ---------- crumbs ---------- */
.yf-crumbs{
  display:flex;flex-wrap:wrap;align-items:center;gap:8px;
  font-family:var(--yf-mono);
  font-size:var(--yf-t14);
  color:var(--yf-mist);
  margin:0 0 24px;
}
.yf-crumbs a{
  color:var(--yf-mist);
  text-decoration:none;
  border-bottom:1px solid rgba(154,167,186,.35);
  transition:color var(--yf-dur) var(--yf-ease),border-color var(--yf-dur) var(--yf-ease);
}
.yf-crumbs a:hover{color:var(--yf-mint);border-bottom-color:currentColor;}
.yf-crumbs__sep{opacity:.5;}
.yf-crumbs [aria-current="page"]{color:var(--yf-snow);}

/* ---------- chapter protocol ---------- */
.yf-chapter{position:relative;}
.yf-chapter__num{
  font-family:var(--yf-mono);
  font-size:var(--yf-t14);
  letter-spacing:0.12em;
  color:var(--yf-mist);
  transition:color 200ms var(--yf-ease);
}
.yf-chapter[data-active] .yf-chapter__num{color:var(--yf-mint);}

/* ---------- media frames ---------- */
.yf-media{
  position:relative;
  display:block;
  overflow:hidden;
  border-radius:var(--yf-radius-m);
  border:1px solid var(--yf-line);
  background:linear-gradient(155deg,var(--yf-panel),#0C1626 70%,#0A1220);
}
.yf-media::after{
  content:"";position:absolute;inset:0;pointer-events:none;
  background-image:
    linear-gradient(90deg,rgba(111,227,196,.07) 1px,transparent 1px),
    linear-gradient(0deg,rgba(111,227,196,.05) 1px,transparent 1px);
  background-size:48px 48px,48px 48px;
  opacity:.55;
}
.yf-media > img,
.yf-media > svg,
.yf-media > picture > img{
  display:block;width:100%;height:100%;
  object-fit:cover;
  position:relative;z-index:1;
}
.yf-media--16x9{aspect-ratio:16/9;}
.yf-media--4x3{aspect-ratio:4/3;}
.yf-media--wide{aspect-ratio:21/9;}
.yf-media--square{aspect-ratio:1/1;}
.yf-media__caption{
  display:block;
  margin-top:10px;
  font-family:var(--yf-mono);
  font-size:var(--yf-t14);
  color:var(--yf-mist);
}

/* ---------- responsive ---------- */
@media (max-width:1080px){
  .yf-nav__link{padding:9px 9px;}
  .yf-nav__link::after{left:9px;right:9px;}
  .yf-header__actions .yf-btn--ghost{padding:9px 14px;}
}

@media (max-width:960px){
  .yf-navtoggle{display:inline-flex;}
  .yf-header__actions{order:2;margin-left:0;}
  .yf-header__actions .yf-btn--ghost{display:none;}

  .yf-nav{
    position:absolute;
    left:0;right:0;top:100%;
    display:none;
    margin-left:0;
    padding:10px 16px 20px;
    background:var(--yf-panel);
    border-bottom:1px solid var(--yf-line);
    box-shadow:0 24px 48px -28px rgba(0,0,0,.95);
  }
  .yf-header[data-open] .yf-nav{display:block;}
  .yf-nav__list{flex-direction:column;align-items:stretch;gap:2px;}
  .yf-nav__link{
    font-size:var(--yf-t18);
    padding:14px 14px;
    border-radius:10px;
    color:var(--yf-snow);
    border-left:2px solid transparent;
  }
  .yf-nav__link::after{display:none;}
  .yf-nav__link:hover{background:rgba(111,227,196,.07);}
  .yf-nav__link[aria-current="page"]{
    border-left-color:var(--yf-lime);
    background:rgba(111,227,196,.10);
    color:var(--yf-snow);
  }

  .yf-brand__sub{display:none;}

  .yf-footer__grid{grid-template-columns:1fr 1fr;}
  .yf-footer__brandcol{grid-column:1 / -1;}
  .yf-footer__legal-links{margin-left:0;}
}

@media (max-width:680px){
  .yf-belt{grid-template-columns:1fr 1fr;}
  .yf-wrap{padding:0 18px;}
  .yf-header__inner{padding:0 18px;gap:12px;}
  .yf-footer__inner{padding:0 18px;}
  .yf-footer__belt{padding:44px 0 4px;}
  .yf-footer__main{padding:44px 0 0;}
  .yf-footer__belt-title{font-size:var(--yf-t22);}
}

@media (max-width:560px){
  .yf-belt{grid-template-columns:1fr;}
  .yf-header__actions .yf-btn--primary{padding:9px 14px;font-size:var(--yf-t14);}
  .yf-brand__name{font-size:var(--yf-t14);}
  .yf-brand__mark{width:32px;height:32px;font-size:var(--yf-t14);}
  .yf-footer__grid{grid-template-columns:1fr;gap:32px;}
  .yf-contact__row{grid-template-columns:38px minmax(0,1fr);}
  .yf-footer__legal{font-size:var(--yf-t14);}
}

@media (prefers-reduced-motion:reduce){
  *,*::before,*::after{
    animation-duration:.001ms!important;
    animation-iteration-count:1!important;
    transition-duration:.001ms!important;
    scroll-behavior:auto!important;
  }
  .yf-belt__item:hover,
  .yf-card:hover,
  .yf-btn:hover{transform:none;}
}