/* ============================================================
   牛宝官网 · 共享样式 /assets/site.css
   色彩配比：钴蓝家族约 55% / 牦牛绒暖白与天光浅蓝约 35%
   藏红约 3%（当前栏目、进度节点、关键 CTA）/ 鎏金 1px 描边
   ============================================================ */

:root{
  --cobalt-deep:#0B3C8C;
  --cobalt-mid:#14549E;
  --cobalt-bright:#2E7BC4;
  --sky:#DCE9F7;
  --yak:#F7F2E8;
  --saffron:#B4342A;
  --gold:#C9A227;
  --ink:#12203A;
  --muted:#5B6B82;
  --surface:#FFFFFF;

  --gold-line:rgba(201,162,39,.55);
  --gold-faint:rgba(201,162,39,.26);
  --hair:rgba(18,32,58,.1);

  --on-deep:#F7F2E8;
  --on-deep-dim:rgba(247,242,232,.72);
  --on-deep-faint:rgba(247,242,232,.4);

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

  --maxw:1280px;
  --gutter:clamp(1.25rem,4vw,3.25rem);
  --header-h:4.75rem;
  --radius:4px;

  --shadow-1:0 1px 2px rgba(18,32,58,.05),0 8px 22px rgba(18,32,58,.06);
  --shadow-2:0 1px 3px rgba(18,32,58,.08);

  --ease:cubic-bezier(.22,.61,.36,1);
  --dur:.32s;
}

/* ---------- reset ---------- */
*,*::before,*::after{box-sizing:border-box}
html{-webkit-text-size-adjust:100%;scroll-behavior:smooth}
body,h1,h2,h3,h4,h5,p,ul,ol,li,figure,blockquote,dl,dd{margin:0}
ul,ol{padding:0;list-style:none}
img,svg,video{display:block;max-width:100%}
button,input,select,textarea{font:inherit;color:inherit}
button{background:none;border:0;cursor:pointer}
a{color:inherit;text-decoration:none}
table{border-collapse:collapse;width:100%}

/* ---------- 基础排版 ---------- */
body{
  font-family:var(--font-sans);
  font-size:1rem;
  line-height:1.9;
  color:var(--ink);
  background:var(--yak);
  -webkit-font-smoothing:antialiased;
  -moz-osx-font-smoothing:grayscale;
  overflow-x:hidden;
}
strong,b{font-weight:600}
::selection{background:var(--sky);color:var(--cobalt-deep)}
[id]{scroll-margin-top:calc(var(--header-h) + 1.5rem)}

:focus-visible{outline:2px solid var(--saffron);outline-offset:3px}
.site-footer :focus-visible,
.section--deep :focus-visible,
.gate-block :focus-visible{outline-color:var(--gold)}

.sr-only{
  position:absolute;width:1px;height:1px;padding:0;margin:-1px;
  overflow:hidden;clip:rect(0 0 0 0);white-space:nowrap;border:0;
}
.skip-link{
  position:fixed;top:.75rem;left:.75rem;z-index:200;
  padding:.7rem 1.1rem;
  background:var(--cobalt-deep);color:var(--yak);
  border:1px solid var(--gold);
  font-size:.875rem;letter-spacing:.06em;
  transform:translateY(-260%);
  transition:transform var(--dur) var(--ease);
}
.skip-link:focus{transform:translateY(0)}

/* ---------- 布局容器 ---------- */
.container{
  width:100%;max-width:var(--maxw);
  margin-inline:auto;padding-inline:var(--gutter);
}
.section{padding-block:clamp(3.5rem,8vw,7rem)}
.section--tight{padding-block:clamp(2rem,4.5vw,3.5rem)}
.section--sky{background:var(--sky)}
.section--yak{background:var(--yak)}
.section--deep{background:var(--cobalt-deep);color:var(--on-deep)}

.grid{display:grid;gap:clamp(1rem,2.4vw,2rem)}
.grid--2{grid-template-columns:repeat(2,minmax(0,1fr))}
.grid--3{grid-template-columns:repeat(3,minmax(0,1fr))}
.grid--4{grid-template-columns:repeat(4,minmax(0,1fr))}

/* ---------- 标题体系 ---------- */
.display{
  font-size:clamp(2.4rem,6vw,5.2rem);
  font-weight:300;
  letter-spacing:-.02em;
  line-height:1.08;
  color:var(--ink);
}
.display--onDeep{color:var(--on-deep)}
.eyebrow{
  font-family:var(--font-mono);
  font-size:.75rem;
  letter-spacing:.28em;
  color:var(--muted);
  line-height:1.6;
}
.section-head{
  display:flex;flex-wrap:wrap;align-items:baseline;
  gap:.5rem clamp(.75rem,2vw,1.4rem);
  margin-bottom:clamp(1.75rem,3vw,2.75rem);
}
.section-head__index{
  font-family:var(--font-mono);
  font-size:.75rem;letter-spacing:.16em;
  color:var(--gold);line-height:1.6;
}
.section-head__title{
  font-size:clamp(1.25rem,2.4vw,1.75rem);
  font-weight:700;line-height:1.45;letter-spacing:.01em;
}
.section-head__desc{
  width:100%;max-width:52ch;
  font-size:.9375rem;line-height:1.85;color:var(--muted);
}
.section--deep .section-head__title{color:var(--on-deep)}
.section--deep .section-head__desc{color:var(--on-deep-dim)}
.section--deep .section-head__index{color:var(--gold)}

.tag-mono{
  display:inline-flex;align-items:center;
  padding:.15rem .5rem;
  font-family:var(--font-mono);
  font-size:.8125rem;letter-spacing:.08em;line-height:1.6;
  color:var(--cobalt-deep);
  background:var(--surface);
  border:1px solid var(--gold-line);
  border-radius:var(--radius);
  white-space:nowrap;
}

.metric{border-left:1px solid var(--gold-line);padding-left:.9rem}
.metric__value{
  display:block;
  font-family:var(--font-mono);
  font-size:clamp(1.25rem,2.6vw,1.75rem);
  line-height:1.4;color:var(--cobalt-deep);letter-spacing:.01em;
}
.metric__label{display:block;font-size:.8125rem;color:var(--muted);line-height:1.7}
.section--deep .metric__value{color:var(--on-deep)}
.section--deep .metric__label{color:var(--on-deep-dim)}

/* ---------- 按钮 ---------- */
.btn{
  display:inline-flex;align-items:center;justify-content:center;gap:.55rem;
  padding:.8rem 1.45rem;
  font-size:.9375rem;letter-spacing:.05em;line-height:1.5;
  border:1px solid transparent;border-radius:var(--radius);
  cursor:pointer;text-align:center;
  transition:background var(--dur) var(--ease),color var(--dur) var(--ease),
             border-color var(--dur) var(--ease),transform var(--dur) var(--ease);
}
.btn--primary{background:var(--saffron);color:#fff;border-color:var(--saffron)}
.btn--primary:hover,.btn--primary:focus-visible{background:#95281f;border-color:#95281f}
.btn--ghost{background:transparent;color:var(--cobalt-deep);border-color:var(--gold-line)}
.btn--ghost:hover,.btn--ghost:focus-visible{border-color:var(--cobalt-deep);color:var(--cobalt-deep)}
.btn--inverse{background:transparent;color:var(--on-deep);border-color:var(--gold-line)}
.btn--inverse:hover,.btn--inverse:focus-visible{border-color:var(--gold);color:var(--gold)}
.btn:active{transform:translateY(1px)}

/* ---------- 面包屑 ---------- */
.breadcrumb{
  display:flex;flex-wrap:wrap;align-items:center;
  gap:.45rem;
  font-family:var(--font-mono);
  font-size:.75rem;letter-spacing:.1em;line-height:1.8;
  color:var(--muted);
}
.breadcrumb a{color:var(--cobalt-mid);transition:color var(--dur) var(--ease)}
.breadcrumb a:hover,.breadcrumb a:focus-visible{color:var(--saffron)}
.breadcrumb__sep{color:var(--gold)}
.breadcrumb [aria-current="page"]{color:var(--ink)}

/* ---------- 正文 ---------- */
.prose{max-width:68ch;font-size:1.0625rem;line-height:1.9}
.prose > * + *{margin-top:1.4em}
.prose h2{
  font-size:clamp(1.25rem,2.2vw,1.6rem);font-weight:700;line-height:1.5;
  margin-top:2.4em;padding-top:.85em;border-top:1px solid var(--gold-faint);
}
.prose h3{font-size:1.125rem;font-weight:600;line-height:1.6;margin-top:2em}
.prose ul li{position:relative;padding-left:1.35rem}
.prose ul li + li{margin-top:.6em}
.prose ul li::before{
  content:"";position:absolute;left:0;top:.95em;
  width:7px;height:1px;background:var(--gold);
}
.prose a{color:var(--cobalt-mid);border-bottom:1px solid var(--gold-line)}
.prose a:hover,.prose a:focus-visible{color:var(--saffron);border-bottom-color:var(--saffron)}
.prose strong{color:var(--cobalt-deep)}

/* ---------- 卡片 ---------- */
.card{
  display:flex;flex-direction:column;
  padding:clamp(1.1rem,2.2vw,1.75rem);
  background:var(--surface);
  border:1px solid var(--hair);
  border-radius:var(--radius);
  box-shadow:var(--shadow-1);
  transition:border-color var(--dur) var(--ease),transform var(--dur) var(--ease),box-shadow var(--dur) var(--ease);
}
.card:hover,.card:focus-within{border-color:var(--gold-line);transform:translateY(-2px)}
.card__index{
  font-family:var(--font-mono);font-size:.75rem;letter-spacing:.14em;
  color:var(--gold);line-height:1.6;
}
.card__title{font-size:1.0625rem;font-weight:700;line-height:1.55;margin-top:.5rem}
.card__desc{font-size:.9375rem;line-height:1.85;color:var(--muted);margin-top:.55rem}
.card__meta{
  margin-top:auto;padding-top:1rem;
  font-family:var(--font-mono);font-size:.75rem;letter-spacing:.08em;
  color:var(--muted);line-height:1.8;
  border-top:1px solid var(--gold-faint);
}

/* ---------- 门洞区块 ---------- */
.gate-block{
  position:relative;overflow:hidden;
  padding:clamp(2.5rem,6vw,4.5rem) clamp(1.5rem,4.5vw,3.5rem) clamp(2rem,4vw,3rem);
  background:var(--cobalt-deep);color:var(--on-deep);
  border:1px solid var(--gold-line);
  border-radius:50% 50% var(--radius) var(--radius) / 17% 17% var(--radius) var(--radius);
}
.gate-block::before{
  content:"";position:absolute;inset:0;pointer-events:none;
  background-image:
    linear-gradient(rgba(247,242,232,.07) 1px,transparent 1px),
    linear-gradient(90deg,rgba(247,242,232,.07) 1px,transparent 1px);
  background-size:48px 48px;
  opacity:.85;
}
.gate-block > *{position:relative;z-index:1}

/* ---------- 图片容器 ---------- */
.media-frame{
  position:relative;overflow:hidden;
  background:var(--sky);
  border:1px solid var(--gold-faint);
  border-radius:var(--radius);
  box-shadow:var(--shadow-2);
}
.media-frame > img,
.media-frame > svg,
.media-frame > picture > img{
  width:100%;height:100%;object-fit:cover;
}
.media-frame--16x9{aspect-ratio:16/9}
.media-frame--4x3{aspect-ratio:4/3}
.media-frame--1x1{aspect-ratio:1/1}
.media-frame--3x4{aspect-ratio:3/4}
.media-caption{
  margin-top:.6rem;
  font-size:.8125rem;line-height:1.75;color:var(--muted);
}

/* ---------- 折叠面板 ---------- */
.accordion{border-top:1px solid var(--gold-faint)}
.accordion__item{border-bottom:1px solid var(--gold-faint)}
.accordion__trigger{
  display:flex;align-items:center;justify-content:space-between;gap:1rem;
  width:100%;padding:1.15rem 1rem 1.15rem 1.1rem;
  border-left:2px solid transparent;text-align:left;
  font-size:1rem;font-weight:600;line-height:1.65;color:var(--ink);
  transition:border-color var(--dur) var(--ease),color var(--dur) var(--ease),background var(--dur) var(--ease);
}
.accordion__trigger:hover{background:rgba(220,233,247,.5)}
.accordion__trigger[aria-expanded="true"]{border-left-color:var(--saffron);color:var(--cobalt-deep)}
.accordion__sign{position:relative;flex:none;width:12px;height:12px}
.accordion__sign::before,.accordion__sign::after{
  content:"";position:absolute;background:var(--gold);
  transition:transform var(--dur) var(--ease),opacity var(--dur) var(--ease);
}
.accordion__sign::before{left:0;top:5.5px;width:12px;height:1px}
.accordion__sign::after{top:0;left:5.5px;width:1px;height:12px}
.accordion__trigger[aria-expanded="true"] .accordion__sign::after{transform:scaleY(0);opacity:0}
.accordion__panel{padding:0 1rem 1.4rem 1.1rem;font-size:.9375rem;line-height:1.9;color:var(--muted)}
.accordion__panel[hidden]{display:none}

/* ---------- 时间线 ---------- */
.timeline{position:relative;padding-left:1.5rem;border-left:1px solid var(--gold-faint)}
.timeline__item{position:relative;padding-bottom:clamp(1.5rem,3vw,2.25rem)}
.timeline__item:last-child{padding-bottom:0}
.timeline__item::before{
  content:"";position:absolute;left:calc(-1.5rem - 4px);top:.55rem;
  width:7px;height:7px;
  background:var(--yak);border:1px solid var(--gold);
  transform:rotate(45deg);
  transition:width var(--dur) var(--ease),height var(--dur) var(--ease);
}
.timeline__date{
  font-family:var(--font-mono);font-size:.75rem;letter-spacing:.12em;
  color:var(--muted);line-height:1.8;
}
.timeline__title{font-weight:700;line-height:1.6;margin-top:.25rem}
.timeline__desc{font-size:.9375rem;line-height:1.85;color:var(--muted);margin-top:.35rem}

/* ---------- 章节索引 ---------- */
.index-rail{
  position:sticky;top:calc(var(--header-h) + 1.5rem);
  display:flex;flex-direction:column;
  padding-left:1rem;border-left:1px solid var(--gold-faint);
  font-family:var(--font-mono);font-size:.75rem;letter-spacing:.1em;
}
.index-rail__link{
  position:relative;
  display:flex;gap:.55rem;align-items:baseline;
  padding:.42rem 0;line-height:1.7;color:var(--muted);
  transition:color var(--dur) var(--ease);
}
.index-rail__link:hover,.index-rail__link:focus-visible{color:var(--cobalt-mid)}
.index-rail__num{color:var(--gold);flex:none}
.index-rail__link.is-current{color:var(--saffron)}
.index-rail__link.is-current .index-rail__num{color:var(--saffron)}
.index-rail__link.is-current::before{
  content:"";position:absolute;left:-1.19rem;top:50%;
  width:7px;height:7px;margin-top:-3.5px;border-radius:50%;
  background:var(--saffron);
}

/* ---------- 六步进度 ---------- */
.step-track{display:flex;gap:.4rem;width:100%}
.step-track__seg{
  flex:1;height:2px;background:rgba(18,32,58,.14);
  transition:background var(--dur) var(--ease);
}
.step-track__seg.is-done{background:var(--cobalt-bright)}
.step-track__seg.is-current{background:var(--saffron)}

/* ---------- 页头 ---------- */
.site-header{
  position:sticky;top:0;z-index:80;
  background:rgba(247,242,232,.94);
  border-bottom:1px solid var(--gold-faint);
  -webkit-backdrop-filter:saturate(140%) blur(8px);
  backdrop-filter:saturate(140%) blur(8px);
  transition:border-color var(--dur) var(--ease),background var(--dur) var(--ease);
}
.site-header__inner{
  display:flex;align-items:center;justify-content:space-between;
  gap:1.5rem;
  width:100%;max-width:var(--maxw);margin-inline:auto;
  min-height:var(--header-h);
  padding:.85rem var(--gutter);
  transition:min-height var(--dur) var(--ease),padding var(--dur) var(--ease);
}
.site-header.is-condensed{border-bottom-color:var(--gold)}
.site-header.is-condensed .site-header__inner{min-height:3.4rem;padding-block:.4rem}

.brand{display:inline-flex;align-items:center;gap:.7rem;flex:none}
.brand__glyph{width:1.4rem;height:1.65rem;flex:none;color:var(--cobalt-deep)}
.brand__text{display:flex;flex-direction:column;line-height:1.2}
.brand__name{
  font-size:1.0625rem;font-weight:700;letter-spacing:.05em;
  color:var(--cobalt-deep);
}
.brand__tag{
  font-family:var(--font-mono);
  font-size:.6875rem;letter-spacing:.22em;
  color:var(--muted);
  transition:opacity var(--dur) var(--ease);
}
.site-header.is-condensed .brand__glyph{height:1.35rem}
.site-header.is-condensed .brand__tag{opacity:.7}

.nav-toggle{
  display:none;align-items:center;gap:.6rem;
  padding:.55rem .8rem;
  color:var(--cobalt-deep);
  border:1px solid var(--gold-line);border-radius:var(--radius);
  font-family:var(--font-mono);font-size:.75rem;letter-spacing:.18em;line-height:1.6;
}
.nav-toggle__bars{display:flex;flex-direction:column;gap:4px;width:18px;flex:none}
.nav-toggle__bars span{
  display:block;height:1px;background:currentColor;
  transition:transform var(--dur) var(--ease),opacity var(--dur) var(--ease);
}
.nav-toggle[aria-expanded="true"] .nav-toggle__bars span:nth-child(1){transform:translateY(5px) rotate(45deg)}
.nav-toggle[aria-expanded="true"] .nav-toggle__bars span:nth-child(2){opacity:0}
.nav-toggle[aria-expanded="true"] .nav-toggle__bars span:nth-child(3){transform:translateY(-5px) rotate(-45deg)}

.site-nav{display:flex;align-items:center}
.nav-list{display:flex;align-items:center;gap:clamp(.9rem,2.2vw,2.1rem)}
.nav-link{
  position:relative;
  display:inline-flex;align-items:center;gap:.45rem;
  padding:.5rem 0;
  font-size:.9375rem;letter-spacing:.03em;line-height:1.6;
  color:var(--ink);
  transition:color var(--dur) var(--ease);
}
.nav-link::before{
  content:"";flex:none;width:5px;height:5px;border-radius:50%;
  background:var(--saffron);
  opacity:0;transform:scale(.4);
  transition:opacity var(--dur) var(--ease),transform var(--dur) var(--ease);
}
.nav-link::after{
  content:"";position:absolute;left:0;right:0;bottom:.25rem;height:1px;
  background:var(--gold);
  transform:scaleX(0);transform-origin:left center;
  transition:transform var(--dur) var(--ease);
}
.nav-link:hover,.nav-link:focus-visible{color:var(--cobalt-mid)}
.nav-link:hover::after,.nav-link:focus-visible::after{transform:scaleX(1)}
.nav-link[aria-current="page"]{color:var(--saffron);font-weight:600}
.nav-link[aria-current="page"]::before{opacity:1;transform:scale(1)}
.nav-link[aria-current="page"]::after{background:var(--saffron);transform:scaleX(1)}

/* ---------- 页脚 ---------- */
.site-footer{
  position:relative;
  background:linear-gradient(180deg,#0B3C8C 0%,#093064 100%);
  color:var(--on-deep);
  border-top:1px solid var(--gold);
}
.site-footer__inner{
  width:100%;max-width:var(--maxw);margin-inline:auto;
  padding:clamp(2.5rem,5vw,4rem) var(--gutter) 0;
}
.footer-brand{
  display:flex;flex-wrap:wrap;align-items:center;gap:.55rem .75rem;
  padding-bottom:1.75rem;
  border-bottom:1px solid var(--gold-faint);
}
.footer-brand__glyph{width:1.6rem;height:1.85rem;flex:none;color:var(--gold)}
.footer-brand__name{font-size:1.05rem;font-weight:700;letter-spacing:.06em;color:var(--yak)}
.footer-brand__line{
  font-family:var(--font-mono);font-size:.6875rem;letter-spacing:.24em;
  color:var(--on-deep-dim);
}
.footer-grid{
  display:grid;grid-template-columns:repeat(4,minmax(0,1fr));
  gap:clamp(1.5rem,3vw,2.75rem);
  padding:2.5rem 0;
}
.footer-col__title{
  margin-bottom:1rem;
  font-family:var(--font-mono);font-size:.6875rem;font-weight:500;
  letter-spacing:.24em;line-height:1.8;color:var(--gold);
}
.footer-col__list{display:flex;flex-direction:column;gap:.6rem;font-size:.9375rem}
.footer-col__list li{line-height:1.7;color:var(--on-deep)}
.footer-link{
  display:inline-block;
  color:var(--on-deep);
  border-bottom:1px solid transparent;
  transition:color var(--dur) var(--ease),border-color var(--dur) var(--ease);
}
.footer-link:hover,.footer-link:focus-visible{color:var(--gold);border-bottom-color:var(--gold)}
.footer-note{
  margin-top:.85rem;
  font-size:.8125rem;line-height:1.8;color:var(--on-deep-dim);
}
.footer-version{display:flex;flex-wrap:wrap;align-items:center;gap:.55rem;margin-bottom:.4rem}
.footer-version .tag-mono{background:transparent;color:var(--yak);border-color:var(--gold-line)}
.footer-version__note{font-size:.8125rem;color:var(--on-deep-dim)}
.footer-bar{
  display:flex;flex-wrap:wrap;align-items:center;justify-content:space-between;
  gap:.5rem 1.5rem;
  padding:1.15rem 0 calc(2rem + env(safe-area-inset-bottom,0px));
  border-top:1px solid var(--gold-faint);
  font-family:var(--font-mono);
  font-size:.75rem;letter-spacing:.06em;line-height:1.9;
  color:var(--on-deep-dim);
}
.footer-bar__item{margin:0}

/* ---------- 返回顶部 ---------- */
.back-to-top{
  position:fixed;right:clamp(1rem,3vw,2.25rem);bottom:clamp(1rem,3vw,2.25rem);z-index:70;
  display:inline-flex;align-items:center;gap:.55rem;
  padding:.7rem 1rem;
  background:var(--cobalt-deep);color:var(--yak);
  border:1px solid var(--gold-line);border-radius:var(--radius);
  font-family:var(--font-mono);font-size:.75rem;letter-spacing:.16em;line-height:1.6;
  opacity:0;visibility:hidden;transform:translateY(10px);
  transition:opacity var(--dur) var(--ease),transform var(--dur) var(--ease),
             visibility var(--dur) var(--ease),border-color var(--dur) var(--ease);
}
.back-to-top.is-visible{opacity:1;visibility:visible;transform:translateY(0)}
.back-to-top:hover,.back-to-top:focus-visible{border-color:var(--gold);color:var(--gold)}
.back-to-top__sign{color:var(--gold);font-size:.9rem;line-height:1}
.back-to-top__label{max-width:9rem;overflow:hidden;text-overflow:ellipsis;white-space:nowrap}

/* ---------- 复制反馈 ---------- */
[data-copy]{cursor:pointer}
[data-copy].is-copied::after{
  content:"已复制";
  margin-left:.5rem;
  font-family:var(--font-mono);font-size:.75rem;letter-spacing:.08em;
  color:var(--gold);
}

/* ---------- 进入显现 ---------- */
html.js-ready [data-reveal]{
  opacity:0;transform:translateY(16px);
  transition:opacity .5s var(--ease),transform .5s var(--ease);
}
html.js-ready [data-reveal].is-visible{opacity:1;transform:none}

/* ---------- 响应式 ---------- */
@media (max-width:1080px){
  .grid--4{grid-template-columns:repeat(2,minmax(0,1fr))}
}
@media (max-width:960px){
  .nav-toggle{display:inline-flex}
  .site-nav{
    position:absolute;left:0;right:0;top:100%;
    display:none;
    padding:.5rem var(--gutter) 1.4rem;
    background:var(--yak);
    border-bottom:1px solid var(--gold-line);
    box-shadow:var(--shadow-1);
  }
  .site-nav[data-open]{display:block}
  .nav-list{flex-direction:column;align-items:stretch;gap:0}
  .nav-list__item{border-bottom:1px dashed var(--gold-faint)}
  .nav-list__item:last-child{border-bottom:0}
  .nav-link{width:100%;padding:.95rem 0;font-size:1rem}
  .nav-link::after{display:none}
  .grid--3{grid-template-columns:repeat(2,minmax(0,1fr))}
  .footer-grid{grid-template-columns:repeat(2,minmax(0,1fr))}
}
@media (max-width:720px){
  .grid--2,.grid--3,.grid--4{grid-template-columns:1fr}
  .back-to-top{bottom:calc(4.75rem + env(safe-area-inset-bottom,0px));right:1rem}
  .back-to-top__label{max-width:6rem}
  .footer-bar{flex-direction:column;align-items:flex-start;gap:.35rem}
}
@media (max-width:520px){
  .footer-grid{grid-template-columns:1fr;gap:1.75rem}
  .brand__tag{letter-spacing:.14em}
  .display{font-size:clamp(2rem,11vw,2.9rem)}
}

/* ---------- 动效降级 ---------- */
@media (prefers-reduced-motion: reduce){
  html{scroll-behavior:auto}
  *,*::before,*::after{
    animation-duration:.01ms !important;
    animation-iteration-count:1 !important;
    transition-duration:.01ms !important;
    scroll-behavior:auto !important;
  }
  html.js-ready [data-reveal]{opacity:1;transform:none}
  .back-to-top{transform:none}
}