/* ==========================================================================
   开元棋盘官方 · 共享样式 /assets/site.css
   基调：棋盘黑 / 暖木棕 / 朱砂红；青瓷绿、琥珀黄、靛青承担分区
   ========================================================================== */

/* 1. 变量 ----------------------------------------------------------------- */
:root{
  --ink:#14110F;
  --ink-soft:#221D19;
  --wood:#8A5A2B;
  --wood-light:#C8A279;
  --cinnabar:#B23A2E;
  --cinnabar-deep:#962D22;
  --amber:#E0A32E;
  --celadon:#5C8D6B;
  --paper:#F6F0E6;
  --paper-deep:#EFE7D9;
  --taupe:#6B6258;
  --indigo:#2E4A57;

  --line:rgba(20,17,15,.12);
  --line-strong:rgba(20,17,15,.24);
  --line-light:rgba(246,240,230,.14);
  --shadow:0 1px 2px rgba(20,17,15,.06);
  --shadow-lift:0 3px 10px rgba(20,17,15,.14);

  --font-display:"Noto Serif SC","Source Han Serif SC","Songti SC","STSong",serif;
  --font-body:"Noto Sans SC","Source Han Sans SC","PingFang SC","Hiragino Sans GB","Microsoft YaHei",system-ui,sans-serif;
  --font-mono:"IBM Plex Mono",ui-monospace,SFMono-Regular,Menlo,Consolas,monospace;

  --rail-w:clamp(320px,36vw,470px);
  --topbar-h:64px;
  --gutter:clamp(20px,3.4vw,52px);
  --ease:cubic-bezier(.2,.7,.2,1);

  --wood-grain:repeating-linear-gradient(115deg,rgba(200,162,121,.055) 0 2px,rgba(200,162,121,0) 2px 9px);
}

/* 2. 重置与基础 ----------------------------------------------------------- */
*,*::before,*::after{box-sizing:border-box}

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

body{
  margin:0;
  min-height:100vh;
  background:var(--paper);
  color:var(--ink);
  font-family:var(--font-body);
  font-size:1.0625rem;
  font-weight:400;
  line-height:1.8;
  letter-spacing:.01em;
  -webkit-font-smoothing:antialiased;
  text-rendering:optimizeLegibility;
  overflow-x:hidden;
}

img,svg,video{max-width:100%;height:auto;display:block}

a{color:var(--wood);text-decoration-thickness:1px;text-underline-offset:.18em}
a:hover{color:var(--cinnabar)}

h1,h2,h3,h4{margin:0;font-family:var(--font-display);font-weight:700;line-height:1.22;letter-spacing:.02em}
p{margin:0 0 1em}
ul,ol{margin:0;padding:0}

:focus-visible{outline:2px solid var(--amber);outline-offset:3px;border-radius:1px}

::selection{background:rgba(224,163,46,.35);color:var(--ink)}

main,#main-content{display:block;padding-top:var(--topbar-h)}

@media (min-width:1121px){
  body{padding-left:var(--rail-w)}
}

/* 3. 通用布局 ------------------------------------------------------------- */
.container{
  width:100%;
  max-width:1120px;
  margin-inline:auto;
  padding-inline:var(--gutter);
}

.grid{display:grid;gap:clamp(20px,3vw,44px)}
.grid--5-7{grid-template-columns:minmax(0,5fr) minmax(0,7fr)}
.grid--4-8{grid-template-columns:minmax(0,4fr) minmax(0,8fr)}

.section{padding-block:clamp(40px,6vw,88px)}
.section--tight{padding-block:clamp(28px,4vw,52px)}

.section-title{
  position:relative;
  font-size:clamp(1.6rem,3vw,2.5rem);
  padding-bottom:.38em;
  margin-bottom:.7em;
}
.section-title::after{
  content:"";
  position:absolute;
  left:0;
  bottom:0;
  height:2px;
  width:clamp(48px,10vw,96px);
  background:var(--wood);
  transform:scaleX(1);
  transform-origin:0 50%;
  transition:transform .26s var(--ease);
}
.section-title[data-underline]:not(.is-inview)::after{transform:scaleX(0)}

.lead{font-size:1.125rem;line-height:1.85;max-width:44ch;color:var(--ink)}

/* 分区色块 */
.zone{padding-block:clamp(40px,6vw,88px);position:relative}
.zone--paper{background:var(--paper)}
.zone--doc{background:var(--paper-deep);border-top:1px solid var(--line);border-bottom:1px solid var(--line)}
.zone--archive{
  background:
    linear-gradient(180deg,rgba(92,141,107,.13),rgba(92,141,107,.04)),
    var(--paper);
  border-top:1px solid rgba(92,141,107,.28);
}
.zone--signup{background:var(--cinnabar);color:var(--paper)}
.zone--signup .section-title::after{background:var(--paper)}
.zone--signup a{color:var(--paper)}
.zone--version{background:var(--amber);color:var(--ink)}
.zone--version .section-title::after{background:var(--ink)}

/* 棋谱网格底纹 */
.board-grid{
  background-image:
    repeating-linear-gradient(to right,rgba(138,90,43,.18) 0 1px,transparent 1px 28px),
    repeating-linear-gradient(to bottom,rgba(138,90,43,.18) 0 1px,transparent 1px 28px);
}

/* 4. 排版组件 ------------------------------------------------------------- */
.kicker{
  display:block;
  font-family:var(--font-body);
  font-weight:700;
  font-size:.95rem;
  letter-spacing:.02em;
  margin-bottom:.4em;
}
.kicker__en{
  display:inline-block;
  margin-left:.6em;
  font-family:var(--font-mono);
  font-size:.72rem;
  font-weight:400;
  letter-spacing:.18em;
  text-transform:uppercase;
  color:var(--taupe);
}

.prose{
  max-width:min(100%,68ch);
  font-size:1rem;
  line-height:1.9;
}
.prose p{margin:0 0 1.15em}
.prose h2,.prose h3{font-size:1.3rem;margin:1.9em 0 .6em}
.prose ul,.prose ol{margin:0 0 1.15em;padding-left:1.25em}
.prose li{margin-bottom:.4em}
.prose a{color:var(--wood)}

.vertical-note{
  writing-mode:vertical-rl;
  font-size:.78rem;
  letter-spacing:.28em;
  color:var(--taupe);
  line-height:1.9;
}

.breadcrumbs{
  font-family:var(--font-mono);
  font-size:.78rem;
  color:var(--taupe);
  margin-bottom:clamp(16px,2.5vw,28px);
}
.breadcrumbs ol{display:flex;flex-wrap:wrap;align-items:center;list-style:none}
.breadcrumbs li{display:flex;align-items:center}
.breadcrumbs li+li::before{content:"›";margin:0 .55em;color:var(--wood-light)}
.breadcrumbs a{color:inherit;text-decoration:none;border-bottom:1px solid transparent}
.breadcrumbs a:hover{color:var(--wood);border-bottom-color:var(--wood)}

.dot{
  display:inline-block;
  width:9px;height:9px;
  border-radius:50%;
  background:var(--wood-light);
  box-shadow:var(--shadow);
  transition:transform .16s var(--ease),background .16s ease,box-shadow .16s ease;
}
.dot--amber{background:var(--amber)}
.dot--celadon{background:var(--celadon)}
.dot--cinnabar{background:var(--cinnabar)}

.tag{
  display:inline-flex;
  align-items:center;
  gap:.45em;
  padding:.24em .7em;
  font-size:.75rem;
  letter-spacing:.12em;
  border-radius:2px;
  background:rgba(92,141,107,.14);
  color:#3E6B4E;
  border:1px solid rgba(92,141,107,.38);
}

/* 5. 按钮 ---------------------------------------------------------------- */
.btn{
  display:inline-flex;
  align-items:center;
  justify-content:center;
  gap:.5em;
  padding:.72em 1.3em;
  font-family:var(--font-body);
  font-weight:700;
  font-size:.95rem;
  line-height:1.2;
  letter-spacing:.02em;
  border:1px solid transparent;
  border-radius:2px;
  text-decoration:none;
  cursor:pointer;
  box-shadow:var(--shadow);
  transition:transform .16s var(--ease),box-shadow .16s ease,background .16s ease,color .16s ease,border-color .16s ease;
}
.btn:hover{transform:translateY(-1px);box-shadow:var(--shadow-lift);text-decoration:none}
.btn:active{transform:translateY(0)}

.btn--cta{background:var(--cinnabar);color:var(--paper)}
.btn--cta:hover{background:var(--cinnabar-deep);color:var(--paper)}

.btn--amber{background:var(--amber);color:var(--ink)}
.btn--amber:hover{background:#C98F1D;color:var(--ink)}

.btn--ghost{
  background:transparent;
  border-color:var(--wood);
  color:var(--ink);
  box-shadow:none;
}
.btn--ghost:hover{border-color:var(--cinnabar);color:var(--cinnabar);background:rgba(178,58,46,.05)}

.btn--ghost-light{
  background:transparent;
  border-color:rgba(246,240,230,.45);
  color:var(--paper);
  box-shadow:none;
}
.btn--ghost-light:hover{border-color:var(--amber);color:var(--amber)}

.btn--sm{padding:.5em .9em;font-size:.82rem}

/* 6. 索引行 / 媒体容器 ---------------------------------------------------- */
.index-list{list-style:none;border-top:1px solid var(--line)}
.index-row{
  display:grid;
  grid-template-columns:minmax(0,5fr) minmax(0,7fr);
  gap:clamp(10px,2vw,32px);
  align-items:baseline;
  padding:clamp(14px,2vw,22px) clamp(8px,1.4vw,16px);
  border-bottom:1px solid var(--line);
  color:inherit;
  text-decoration:none;
  transition:background .16s ease;
}
.index-row:hover{background:rgba(200,162,121,.08);color:inherit}
.index-row__title{font-family:var(--font-display);font-weight:700;font-size:1.125rem;line-height:1.4}
.index-row__meta{
  font-family:var(--font-mono);
  font-size:.75rem;
  letter-spacing:.08em;
  color:var(--taupe);
}
.index-row__body{font-size:.95rem;line-height:1.8;color:var(--taupe);margin:0}

.media{
  position:relative;
  display:block;
  width:100%;
  margin:0;
  overflow:hidden;
  background-color:var(--ink-soft);
  background-image:
    repeating-linear-gradient(to right,rgba(200,162,121,.16) 0 1px,transparent 1px 26px),
    repeating-linear-gradient(to bottom,rgba(200,162,121,.16) 0 1px,transparent 1px 26px),
    var(--wood-grain);
  box-shadow:var(--shadow);
  border:1px solid var(--line);
}
.media__img,
.media img{
  display:block;
  width:100%;
  height:100%;
  object-fit:cover;
}
.media--16x9{aspect-ratio:16/9}
.media--4x5{aspect-ratio:4/5}
.media--1x1{aspect-ratio:1/1}
.media--wide{aspect-ratio:21/9}
.media__caption{
  margin-top:.6em;
  font-size:.78rem;
  line-height:1.65;
  color:var(--taupe);
}

/* 7. 页头 ---------------------------------------------------------------- */
.site-header{position:relative;z-index:100}

.skip-link{
  position:fixed;
  top:10px;
  left:10px;
  z-index:200;
  padding:.7em 1.1em;
  background:var(--ink);
  color:var(--paper);
  font-weight:700;
  font-size:.9rem;
  text-decoration:none;
  border-radius:2px;
  box-shadow:var(--shadow-lift);
  transform:translateY(-180%);
  transition:transform .2s var(--ease);
}
.skip-link:focus,
.skip-link:focus-visible{transform:translateY(0);color:var(--paper)}

/* 顶栏 */
.topbar{
  position:fixed;
  top:0;
  right:0;
  left:0;
  z-index:90;
  height:var(--topbar-h);
  display:flex;
  align-items:center;
  gap:clamp(10px,2vw,28px);
  padding-inline:var(--gutter);
  background:rgba(246,240,230,.94);
  border-bottom:1px solid var(--line);
  backdrop-filter:saturate(120%) blur(6px);
}
.topbar__actions{
  display:flex;
  align-items:center;
  gap:clamp(10px,1.8vw,26px);
  margin-left:auto;
}
.topbar__link{
  font-size:.85rem;
  font-weight:700;
  color:var(--ink);
  text-decoration:none;
  border-bottom:1px solid transparent;
  transition:color .16s ease,border-color .16s ease;
}
.topbar__link:hover{color:var(--celadon);border-bottom-color:var(--celadon)}

/* 品牌 */
.brand{
  display:inline-flex;
  align-items:center;
  gap:.6em;
  color:inherit;
  text-decoration:none;
  line-height:1.15;
}
.brand:hover{color:inherit;text-decoration:none}
.brand__mark{
  flex:0 0 auto;
  width:22px;
  height:22px;
  border-radius:50%;
  background:radial-gradient(circle at 34% 28%,#FFFFFF 0%,#EBE2D2 42%,#C2B49D 78%,#9E9078 100%);
  box-shadow:0 0 0 1px rgba(20,17,15,.35),inset 0 -1px 2px rgba(20,17,15,.25);
  transition:transform .16s var(--ease),box-shadow .16s ease;
}
.brand:hover .brand__mark{transform:translateY(-2px);box-shadow:0 0 0 1px rgba(20,17,15,.35),0 4px 8px rgba(20,17,15,.28)}
.brand__text{display:flex;flex-direction:column;gap:.4em}
.brand__name{
  font-family:var(--font-display);
  font-weight:700;
  font-size:clamp(1.1rem,1.5vw,1.42rem);
  letter-spacing:.04em;
}
.brand__tagline{
  font-size:.72rem;
  letter-spacing:.14em;
  color:var(--taupe);
}
.brand--compact{display:none}

/* 版本切换通道 */
.version-switch{display:flex;align-items:center;gap:.6em}
.version-switch__label{
  font-size:.72rem;
  letter-spacing:.16em;
  color:var(--taupe);
  white-space:nowrap;
}
.version-switch__track{
  display:inline-flex;
  padding:2px;
  border:1px solid var(--wood-light);
  border-radius:2px;
  background:rgba(255,255,255,.5);
}
.version-switch__opt{
  appearance:none;
  border:0;
  background:transparent;
  color:var(--taupe);
  font-family:var(--font-body);
  font-size:.78rem;
  font-weight:700;
  letter-spacing:.04em;
  padding:.42em .78em;
  border-radius:1px;
  cursor:pointer;
  transition:background .16s ease,color .16s ease;
}
.version-switch__opt:hover{background:rgba(200,162,121,.2);color:var(--ink)}
.version-switch__opt.is-active{background:var(--amber);color:var(--ink)}

/* 移动菜单按钮 */
.nav-toggle{
  display:none;
  align-items:center;
  gap:.55em;
  padding:.5em .8em;
  background:transparent;
  border:1px solid var(--line-strong);
  border-radius:2px;
  color:var(--ink);
  font-family:var(--font-body);
  font-size:.82rem;
  font-weight:700;
  letter-spacing:.04em;
  cursor:pointer;
  transition:border-color .16s ease,background .16s ease;
}
.nav-toggle:hover{border-color:var(--wood);background:rgba(200,162,121,.12)}
.nav-toggle__bars{
  display:block;
  width:16px;
  height:2px;
  background:currentColor;
  box-shadow:0 5px 0 currentColor,0 -5px 0 currentColor;
  transition:box-shadow .16s ease;
}
.nav-toggle[aria-expanded="true"]{border-color:var(--cinnabar);color:var(--cinnabar)}
.nav-toggle[aria-expanded="true"] .nav-toggle__bars{box-shadow:-6px 0 0 currentColor,6px 0 0 currentColor}

/* 栏目轴 */
.rail{
  position:fixed;
  top:0;
  left:0;
  z-index:100;
  width:var(--rail-w);
  height:100vh;
  display:flex;
  flex-direction:column;
  gap:clamp(18px,3vh,38px);
  padding:clamp(22px,3.2vh,42px) clamp(20px,2.4vw,38px);
  background-color:var(--ink);
  background-image:var(--wood-grain);
  color:var(--paper);
  overflow-y:auto;
  overscroll-behavior:contain;
}
.rail__head{display:flex;align-items:flex-start;gap:12px}
.brand--rail{color:var(--paper)}
.brand--rail .brand__tagline{color:rgba(246,240,230,.55)}
.brand--rail .brand__mark{box-shadow:0 0 0 1px rgba(246,240,230,.3),inset 0 -1px 2px rgba(20,17,15,.25)}
.rail__close{
  display:none;
  margin-left:auto;
  width:34px;
  height:34px;
  place-items:center;
  background:transparent;
  border:1px solid rgba(246,240,230,.3);
  border-radius:2px;
  color:var(--paper);
  font-size:1.1rem;
  line-height:1;
  cursor:pointer;
}
.rail__close:hover{border-color:var(--amber);color:var(--amber)}

.nav{display:flex;flex-direction:column;gap:.8em}
.nav__label{
  display:flex;
  align-items:baseline;
  gap:.6em;
  margin:0;
  font-size:.82rem;
  font-weight:700;
  letter-spacing:.1em;
  color:rgba(246,240,230,.66);
}
.nav__label-en{
  font-family:var(--font-mono);
  font-size:.68rem;
  font-weight:400;
  letter-spacing:.2em;
  color:rgba(246,240,230,.4);
}
.nav__list{
  list-style:none;
  display:flex;
  flex-direction:column;
  border-top:1px solid var(--line-light);
}
.nav__item{border-bottom:1px solid var(--line-light)}
.nav__link{
  position:relative;
  display:flex;
  align-items:center;
  gap:.8em;
  padding:.86em .4em;
  color:rgba(246,240,230,.82);
  text-decoration:none;
  font-size:1rem;
  font-weight:700;
  letter-spacing:.02em;
  transition:color .16s ease,background .16s ease,padding-left .16s var(--ease);
}
.nav__link::before{
  content:"";
  flex:0 0 auto;
  width:9px;
  height:9px;
  border-radius:50%;
  background:rgba(200,162,121,.45);
  box-shadow:inset 0 -1px 1px rgba(20,17,15,.4);
  transition:transform .16s var(--ease),background .16s ease,box-shadow .16s ease;
}
.nav__link:hover{color:#fff;background:rgba(200,162,121,.08);padding-left:.7em}
.nav__link:hover::before{background:var(--wood-light);transform:translateY(-2px);box-shadow:0 3px 6px rgba(0,0,0,.4)}
.nav__en{
  margin-left:auto;
  font-family:var(--font-mono);
  font-size:.66rem;
  font-weight:400;
  letter-spacing:.18em;
  color:rgba(246,240,230,.4);
  transition:color .16s ease;
}
.nav__link[aria-current="page"]{
  color:#fff;
  background:rgba(224,163,46,.13);
  padding-left:.7em;
}
.nav__link[aria-current="page"]::before{
  background:var(--amber);
  transform:translateY(-2px);
  box-shadow:0 0 0 3px rgba(224,163,46,.22);
}
.nav__link[aria-current="page"] .nav__en{color:var(--amber)}
.nav__link:focus-visible{outline-color:var(--amber)}

.rail__foot{
  margin-top:auto;
  display:flex;
  align-items:center;
  justify-content:space-between;
  gap:12px;
  padding-top:1em;
  border-top:1px solid var(--line-light);
  font-family:var(--font-mono);
  font-size:.72rem;
  letter-spacing:.08em;
  color:rgba(246,240,230,.5);
}
.rail__note{margin:0}
.rail__coord{color:rgba(246,240,230,.38);white-space:nowrap}

.nav-scrim{display:none}

/* 8. 页脚 ---------------------------------------------------------------- */
.site-footer{
  position:relative;
  background-color:var(--ink);
  background-image:var(--wood-grain);
  color:rgba(246,240,230,.78);
  border-top:1px solid rgba(138,90,43,.55);
}
.footer__grid{
  display:grid;
  grid-template-columns:1.6fr 1fr 1fr 1.35fr;
  gap:clamp(24px,3vw,56px);
  padding:clamp(40px,6vw,78px) var(--gutter) clamp(28px,4vw,48px);
  max-width:1240px;
  margin-inline:auto;
}
.brand--footer{color:var(--paper);margin-bottom:1.1em}
.brand--footer .brand__tagline{color:rgba(246,240,230,.52)}
.brand--footer .brand__mark{box-shadow:0 0 0 1px rgba(246,240,230,.3),inset 0 -1px 2px rgba(20,17,15,.25)}
.footer__site{
  font-family:var(--font-mono);
  font-size:.76rem;
  letter-spacing:.08em;
  color:rgba(246,240,230,.55);
  margin:0 0 1.1em;
}
.footer__closing{
  margin:0;
  max-width:34ch;
  padding-left:14px;
  border-left:2px solid var(--wood-light);
  font-size:.9rem;
  line-height:1.9;
  color:rgba(246,240,230,.72);
}
.footer__title{
  font-family:var(--font-body);
  font-size:.78rem;
  font-weight:700;
  letter-spacing:.2em;
  color:var(--wood-light);
  margin:0 0 1em;
  padding-bottom:.7em;
  border-bottom:1px solid var(--line-light);
}
.footer__list{list-style:none;display:flex;flex-direction:column;gap:.55em}
.footer__list a{
  color:rgba(246,240,230,.78);
  text-decoration:none;
  font-size:.92rem;
  border-bottom:1px solid transparent;
  transition:color .16s ease,border-color .16s ease,padding-left .16s var(--ease);
}
.footer__list a:hover{color:var(--amber);border-bottom-color:rgba(224,163,46,.55);padding-left:.25em}
.footer__meta{
  margin:0 0 .45em;
  font-family:var(--font-mono);
  font-size:.76rem;
  line-height:1.7;
  letter-spacing:.02em;
  color:rgba(246,240,230,.55);
  word-break:break-word;
}
.footer__col--contact .footer__list{margin-bottom:1.2em}

.footer__base{
  display:flex;
  flex-wrap:wrap;
  align-items:center;
  gap:clamp(12px,2vw,32px);
  max-width:1240px;
  margin-inline:auto;
  padding:clamp(16px,2.4vw,24px) var(--gutter);
  border-top:1px solid var(--line-light);
  font-family:var(--font-mono);
  font-size:.74rem;
  letter-spacing:.06em;
  color:rgba(246,240,230,.5);
}
.footer__legal,.footer__copy{margin:0}
.footer__legal-links{
  list-style:none;
  display:flex;
  flex-wrap:wrap;
  gap:clamp(10px,1.6vw,22px);
  margin-left:auto;
}
.footer__legal-links a{color:rgba(246,240,230,.62);text-decoration:none}
.footer__legal-links a:hover{color:var(--amber)}

/* 9. 阅读进度条 ----------------------------------------------------------- */
.read-progress{
  position:fixed;
  top:0;
  left:0;
  width:100%;
  height:2px;
  transform:scaleX(0);
  transform-origin:0 50%;
  background:var(--amber);
  z-index:130;
  pointer-events:none;
  transition:transform .06s linear;
}

/* 10. 新版 / 2024 版演示态 ------------------------------------------------ */
html[data-version="2024"] .rail{background-color:var(--ink-soft);box-shadow:inset -1px 0 0 rgba(224,163,46,.35)}
html[data-version="2024"] .nav__list{flex-direction:column-reverse}
html[data-version="2024"] .nav__label-en{color:rgba(224,163,46,.6)}
html[data-version="2024"] .rail__coord{color:var(--amber)}
html[data-version="2024"] .version-switch__opt.is-active{background:var(--indigo);color:var(--paper)}
html[data-version="2024"] .version-switch__track{border-color:var(--indigo)}

/* 11. 响应式 -------------------------------------------------------------- */
@media (min-width:1121px){
  .topbar{left:var(--rail-w)}
}

@media (max-width:1120px){
  :root{--topbar-h:58px}

  .topbar{justify-content:flex-start;gap:10px;padding-inline:16px}
  .brand--compact{display:inline-flex;order:1}
  .brand--compact .brand__name{font-size:1.02rem}
  .brand--compact .brand__mark{width:18px;height:18px}
  .topbar__actions{order:2;gap:10px}
  .nav-toggle{display:inline-flex;order:3;margin-left:4px}
  .version-switch__label{display:none}
  .version-switch__opt{padding:.4em .62em;font-size:.74rem}

  .rail{
    width:min(88vw,360px);
    z-index:120;
    transform:translateX(-102%);
    visibility:hidden;
    box-shadow:0 0 40px rgba(0,0,0,.45);
    transition:transform .24s var(--ease),visibility .24s linear;
  }
  .site-header[data-open] .rail{transform:translateX(0);visibility:visible}
  .rail__close{display:grid}

  .nav-scrim{
    display:block;
    position:fixed;
    inset:0;
    z-index:95;
    background:rgba(20,17,15,.55);
    opacity:0;
    visibility:hidden;
    transition:opacity .2s ease,visibility .2s linear;
  }
  .site-header[data-open] .nav-scrim{opacity:1;visibility:visible}

  .footer__grid{grid-template-columns:repeat(2,minmax(0,1fr))}
  .footer__col--contact{grid-column:span 2}
  .footer__legal-links{margin-left:0}
}

@media (max-width:880px){
  .grid--5-7,.grid--4-8{grid-template-columns:minmax(0,1fr)}
  .index-row{grid-template-columns:minmax(0,1fr);gap:.35em}
}

@media (max-width:720px){
  body{font-size:1rem}
  .topbar__link{display:none}
  .topbar__actions{gap:8px}
  .footer__grid{grid-template-columns:minmax(0,1fr);gap:28px}
  .footer__col--contact{grid-column:auto}
  .footer__closing{max-width:none}
  .footer__base{flex-direction:column;align-items:flex-start}
  .vertical-note{display:none}
}

@media (max-width:420px){
  .nav-toggle__label{display:none}
  .version-switch__opt{padding:.4em .5em}
}

/* 12. 动效降级 ------------------------------------------------------------ */
@media (prefers-reduced-motion:reduce){
  html{scroll-behavior:auto}
  *,*::before,*::after{
    animation-duration:.001ms !important;
    animation-iteration-count:1 !important;
    transition-duration:.001ms !important;
    transition-delay:0ms !important;
  }
  .btn:hover,.brand:hover .brand__mark,.nav__link:hover::before{transform:none}
  .read-progress{transition:none}
}