/* AI 知识闯关 · 统一设计系统（样张）
 * 零框架 / 零外部字体 / 零 CDN：单文件 CSS，树莓派与移动端都轻。
 * 换肤只需改 :root 或 body[data-theme] 的 --acc / --ac2 两个变量。
 */
:root{
  --bg:#070b16; --bg2:#0b1020; --bg3:#101830;
  --surface:rgba(255,255,255,.045); --surface2:rgba(255,255,255,.075);
  --line:rgba(255,255,255,.10); --line2:rgba(255,255,255,.18);
  --txt:#eaf0ff; --muted:#9aa7c2; --dim:#6d7896;
  --acc:#4de3ff; --ac2:#8b7dff;
  --ok:#5ce6a8; --no:#ff7b7b; --warn:#ffc46b;
  --r:18px; --r2:12px; --maxw:1180px;
  --shadow:0 18px 60px rgba(0,0,0,.45);
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{
  margin:0; background:var(--bg); color:var(--txt);
  font-family:-apple-system,BlinkMacSystemFont,"Segoe UI","PingFang SC","Microsoft YaHei",sans-serif;
  font-size:16px; line-height:1.75; -webkit-font-smoothing:antialiased;
  overflow-x:hidden;
}
a{color:inherit; text-decoration:none}
img{max-width:100%; display:block}
button{font:inherit; cursor:pointer}
::selection{background:rgba(77,227,255,.28); color:#fff}

/* ---------- 背景层：纯 CSS 辉光 + 细网格，不用 canvas/粒子 ---------- */
.bg-fx{position:fixed; inset:0; z-index:-1; pointer-events:none; overflow:hidden;
  background:radial-gradient(1100px 700px at 12% -8%, rgba(77,227,255,.11), transparent 62%),
             radial-gradient(900px 620px at 88% 8%, rgba(139,125,255,.13), transparent 60%),
             linear-gradient(180deg,var(--bg) 0%,var(--bg2) 45%,var(--bg) 100%);}
.bg-fx::before{content:""; position:absolute; inset:0; opacity:.35;
  background-image:linear-gradient(rgba(255,255,255,.035) 1px,transparent 1px),
                   linear-gradient(90deg,rgba(255,255,255,.035) 1px,transparent 1px);
  background-size:44px 44px;
  mask-image:linear-gradient(180deg,#000 0%,rgba(0,0,0,.35) 60%,transparent 100%);}
.bg-fx .orb{position:absolute; border-radius:50%; filter:blur(90px); opacity:.30; animation:float 18s ease-in-out infinite}
.bg-fx .orb.a{width:420px;height:420px;background:var(--acc);left:-120px;top:18%}
.bg-fx .orb.b{width:380px;height:380px;background:var(--ac2);right:-100px;top:52%;animation-delay:-7s}
@keyframes float{0%,100%{transform:translate3d(0,0,0) scale(1)}50%{transform:translate3d(28px,-36px,0) scale(1.08)}}

.wrap{max-width:var(--maxw); margin:0 auto; padding:0 24px}
.sec{padding:76px 0 8px; position:relative}
.sec-head{margin-bottom:28px}
.eyebrow{display:inline-flex;align-items:center;gap:8px;font-size:12px;letter-spacing:.22em;
  color:var(--acc);text-transform:uppercase;font-weight:700;
  padding:5px 12px;border:1px solid color-mix(in srgb,var(--acc) 35%,transparent);
  border-radius:999px;background:color-mix(in srgb,var(--acc) 8%,transparent)}
.eyebrow::before{content:"";width:6px;height:6px;border-radius:50%;background:var(--acc);box-shadow:0 0 12px var(--acc)}
h1,h2,h3{line-height:1.3;letter-spacing:-.02em;margin:0}
.sec-title{font-size:clamp(24px,3.2vw,36px);font-weight:800;margin:14px 0 8px}
.sec-desc{color:var(--muted);max-width:720px;margin:0;font-size:15px}
.gtext{background:linear-gradient(100deg,var(--acc),var(--ac2) 60%,#ff8fd0);
  -webkit-background-clip:text;background-clip:text;color:transparent}
.muted{color:var(--muted)} .dim{color:var(--dim)}
.divider{height:1px;background:var(--line);margin:56px 0}

/* ---------- 顶栏 ---------- */
.topbar{position:sticky;top:0;z-index:50;
  background:rgba(7,11,22,.78);backdrop-filter:blur(18px);
  border-bottom:1px solid var(--line)}
.topbar .wrap{display:flex;align-items:center;gap:26px;height:68px}
.brand{display:flex;align-items:center;gap:11px;font-weight:800;font-size:17px;white-space:nowrap;letter-spacing:.02em}
.brand img{width:38px;height:38px;border-radius:11px;box-shadow:0 0 0 1px var(--line2),0 6px 20px rgba(77,227,255,.22)}
.brand small{display:block;font-size:10px;letter-spacing:.28em;color:var(--dim);font-weight:600;line-height:1}
.nav{display:flex;gap:4px;flex:1;min-width:0;overflow:auto;scrollbar-width:none}
.nav::-webkit-scrollbar{display:none}
.nav a{padding:7px 13px;border-radius:9px;font-size:14px;color:var(--muted);white-space:nowrap;transition:.2s}
.nav a:hover{color:var(--txt);background:var(--surface)}
.nav a.on{color:var(--acc);background:color-mix(in srgb,var(--acc) 10%,transparent)}
.top-cta{display:flex;gap:10px}
.btn{display:inline-flex;align-items:center;justify-content:center;gap:8px;
  padding:11px 20px;border-radius:11px;border:1px solid var(--line2);
  background:var(--surface);color:var(--txt);font-size:14px;font-weight:650;
  transition:transform .18s,box-shadow .22s,background .22s,border-color .22s;white-space:nowrap}
.btn:hover{transform:translateY(-2px);border-color:color-mix(in srgb,var(--acc) 55%,transparent);background:var(--surface2)}
.btn.primary{border:none;color:#06101c;font-weight:800;
  background:linear-gradient(100deg,var(--acc),var(--ac2));
  box-shadow:0 8px 30px color-mix(in srgb,var(--acc) 28%,transparent)}
.btn.primary:hover{box-shadow:0 12px 38px color-mix(in srgb,var(--acc) 45%,transparent)}
.btn.ghost{background:transparent}
.btn.sm{padding:8px 14px;font-size:13px;border-radius:9px}
.btn[disabled]{opacity:.42;cursor:not-allowed;transform:none}
.kbd{font:600 11px ui-monospace,SFMono-Regular,Consolas,monospace;color:var(--dim);
  border:1px solid var(--line);border-radius:5px;padding:1px 6px;background:rgba(255,255,255,.04)}

/* ---------- 卡片 / 徽章 ---------- */
.card{background:var(--surface);border:1px solid var(--line);border-radius:var(--r);
  padding:24px;box-shadow:var(--shadow);position:relative;overflow:hidden}
.card.hover{transition:transform .25s,border-color .25s,background .25s}
.card.hover:hover{transform:translateY(-5px);border-color:color-mix(in srgb,var(--acc) 42%,transparent);background:var(--surface2)}
.badge{display:inline-flex;align-items:center;gap:6px;font-size:12px;font-weight:700;
  padding:4px 10px;border-radius:999px;border:1px solid var(--line2);
  background:rgba(255,255,255,.04);color:var(--muted)}
.badge.acc{color:var(--acc);border-color:color-mix(in srgb,var(--acc) 40%,transparent);
  background:color-mix(in srgb,var(--acc) 9%,transparent)}
.badge.warn{color:var(--warn);border-color:color-mix(in srgb,var(--warn) 40%,transparent)}
.chip{display:inline-flex;align-items:center;gap:7px;padding:7px 14px;border-radius:999px;
  border:1px solid var(--line);background:var(--surface);color:var(--muted);
  font-size:13px;font-weight:650;transition:.2s;cursor:pointer}
.chip:hover{color:var(--txt);border-color:var(--line2)}
.chip.on{color:#06101c;background:linear-gradient(100deg,var(--acc),var(--ac2));border-color:transparent;font-weight:800}

/* ---------- 首页 hero ---------- */
.hero{padding:76px 0 54px}
.hero-grid{display:grid;grid-template-columns:1.15fr .85fr;gap:56px;align-items:center}
.hero h1{font-size:clamp(34px,5.1vw,62px);font-weight:850;letter-spacing:-.045em;margin:20px 0}
.hero .lead{font-size:17px;color:var(--muted);max-width:560px;margin:0 0 26px}
.hero-actions{display:flex;gap:12px;flex-wrap:wrap;margin-bottom:34px}
.stat-strip{display:flex;gap:10px;flex-wrap:wrap}
.stat{min-width:104px;padding:12px 16px;border:1px solid var(--line);border-radius:13px;background:var(--surface)}
.stat b{display:block;font:800 24px/1.2 ui-monospace,SFMono-Regular,Consolas,monospace;color:var(--acc)}
.stat span{font-size:12px;color:var(--dim)}
.hero-visual{position:relative;min-height:420px}
.hero-visual .panel{position:absolute;border:1px solid var(--line2);border-radius:18px;
  background:linear-gradient(145deg,rgba(20,28,52,.95),rgba(10,15,30,.95));
  box-shadow:0 24px 70px rgba(0,0,0,.55);padding:16px 18px;backdrop-filter:blur(8px)}
.hero-visual .p1{inset:8px 80px 215px 0;transform:rotate(-2deg);animation:floats 7s ease-in-out infinite}
.hero-visual .p2{right:0;bottom:2px;width:64%;transform:rotate(1.6deg);animation:floats 8s ease-in-out infinite reverse}
@keyframes floats{0%,100%{translate:0 0}50%{translate:0 -12px}}
.panel .pl{display:flex;gap:6px;margin-bottom:12px}
.panel .pl i{width:8px;height:8px;border-radius:50%;background:#ff6b6b;opacity:.7}
.panel .pl i:nth-child(2){background:#ffc46b}.panel .pl i:nth-child(3){background:#5ce6a8}
.panel .code{font:12.5px/1.75 ui-monospace,SFMono-Regular,Consolas,monospace;color:#b8c6ea}
.panel .code em{color:var(--acc);font-style:normal}
.panel .code b{color:var(--ac2);font-weight:600}
.panel .mini{font-size:13px;color:var(--muted)}
.panel .mini strong{color:var(--ok)}
.p2 .rowline{display:flex;align-items:center;gap:10px;margin:6px 0}
.p2 .rowline i{width:26px;height:26px;border-radius:8px;background:color-mix(in srgb,var(--acc) 20%,transparent);
  display:grid;place-items:center;color:var(--acc);font-style:normal;font-size:12px;font-weight:800}

/* ---------- 答题主控件 ---------- */
.quiz-shell{max-width:820px;margin:0 auto}
.quiz-card{padding:30px;background:linear-gradient(160deg,rgba(255,255,255,.065),rgba(255,255,255,.025));
  border:1px solid var(--line2);border-radius:22px;box-shadow:var(--shadow);position:relative;overflow:hidden}
.quiz-card::before{content:"";position:absolute;top:0;left:0;right:0;height:2px;
  background:linear-gradient(90deg,transparent,var(--acc),var(--ac2),transparent)}
.quiz-top{display:flex;align-items:center;justify-content:space-between;gap:12px;flex-wrap:wrap;margin-bottom:18px}
.quiz-meta{display:flex;gap:8px;flex-wrap:wrap}
.progress{height:5px;border-radius:99px;background:rgba(255,255,255,.08);overflow:hidden;margin:0 0 24px}
.progress .bar{height:100%;width:0;border-radius:99px;background:linear-gradient(90deg,var(--acc),var(--ac2));
  transition:width .45s cubic-bezier(.2,.8,.2,1);box-shadow:0 0 14px var(--acc)}
.q-stem{font-size:clamp(19px,2.4vw,25px);font-weight:750;line-height:1.6;margin:0 0 8px;letter-spacing:-.01em}
.q-hint{font-size:13px;color:var(--dim);margin:0 0 20px}
.opts{display:grid;gap:11px}
.opt{display:flex;align-items:flex-start;gap:14px;width:100%;text-align:left;
  padding:15px 18px;border-radius:13px;border:1px solid var(--line);
  background:rgba(255,255,255,.035);color:var(--txt);font-size:15px;line-height:1.6;
  transition:transform .16s,border-color .2s,background .2s,box-shadow .2s}
.opt:hover{transform:translateX(4px);border-color:var(--line2);background:rgba(255,255,255,.07)}
.opt .key{flex:0 0 28px;height:28px;border-radius:8px;display:grid;place-items:center;
  font:800 13px ui-monospace,monospace;color:var(--muted);
  border:1px solid var(--line2);background:rgba(255,255,255,.04);transition:.2s}
.opt .txt{flex:1;padding-top:1px}
.opt.sel{border-color:var(--acc);background:color-mix(in srgb,var(--acc) 11%,transparent);
  box-shadow:inset 0 0 0 1px color-mix(in srgb,var(--acc) 25%,transparent)}
.opt.sel .key{background:var(--acc);color:#06101c;border-color:transparent}
.opt.right{border-color:var(--ok);background:color-mix(in srgb,var(--ok) 12%,transparent);animation:pop .35s}
.opt.right .key{background:var(--ok);color:#04140d;border-color:transparent}
.opt.wrong{border-color:var(--no);background:color-mix(in srgb,var(--no) 12%,transparent)}
.opt.wrong .key{background:var(--no);color:#1b0606;border-color:transparent}
.opt[disabled]{cursor:default;transform:none!important}
@keyframes pop{0%{transform:scale(1)}45%{transform:scale(1.015)}100%{transform:scale(1)}}
.quiz-foot{display:flex;align-items:center;justify-content:space-between;gap:12px;margin-top:22px;flex-wrap:wrap}
.quiz-foot .left{font-size:13px;color:var(--dim)}
.feedback{margin-top:20px;border-radius:14px;padding:18px 20px;display:none;
  border:1px solid var(--line2);background:rgba(255,255,255,.045);animation:slidein .35s ease}
.feedback.show{display:block}
.feedback.ok{border-color:color-mix(in srgb,var(--ok) 45%,transparent);background:color-mix(in srgb,var(--ok) 8%,transparent)}
.feedback.no{border-color:color-mix(in srgb,var(--no) 45%,transparent);background:color-mix(in srgb,var(--no) 8%,transparent)}
@keyframes slidein{from{opacity:0;transform:translateY(10px)}to{opacity:1;transform:none}}
.fb-title{font-weight:800;font-size:16px;margin-bottom:6px;display:flex;align-items:center;gap:9px}
.feedback.ok .fb-title{color:var(--ok)} .feedback.no .fb-title{color:var(--no)}
.fb-body{font-size:14px;color:var(--muted);line-height:1.8}
.fb-body a{color:var(--acc);text-decoration:underline;text-underline-offset:3px}

/* ---------- 随机内链 / 大类卡片 ---------- */
.roam-grid{display:grid;grid-template-columns:repeat(5,1fr);gap:12px}
.roam-card{display:block;padding:16px;border-radius:14px;border:1px solid var(--line);
  background:var(--surface);transition:.22s;min-height:104px;position:relative;overflow:hidden}
.roam-card::after{content:"↗";position:absolute;right:14px;top:12px;color:var(--dim);font-size:14px;transition:.22s}
.roam-card:hover{transform:translateY(-4px);border-color:color-mix(in srgb,var(--acc) 45%,transparent);background:var(--surface2)}
.roam-card:hover::after{color:var(--acc);transform:translate(2px,-2px)}
.roam-tag{font-size:11px;color:var(--acc);letter-spacing:.12em;font-weight:700}
.roam-card b{display:block;font-size:14px;line-height:1.5;margin-top:8px;padding-right:14px}
.cat-grid{display:grid;grid-template-columns:repeat(4,1fr);gap:14px}
.cat-card{padding:20px;border-radius:16px;border:1px solid var(--line);background:var(--surface);
  position:relative;transition:.24s;min-height:186px;display:flex;flex-direction:column}
.cat-card:hover{transform:translateY(-5px);border-color:var(--line2);background:var(--surface2)}
.cat-card.live{border-color:color-mix(in srgb,var(--acc) 40%,transparent);
  background:linear-gradient(150deg,color-mix(in srgb,var(--acc) 10%,transparent),var(--surface))}
.cat-card.live::before{content:"";position:absolute;inset:0;border-radius:16px;pointer-events:none;
  box-shadow:inset 0 0 40px color-mix(in srgb,var(--acc) 8%,transparent)}
.cat-no{font:700 11px ui-monospace,monospace;color:var(--dim);letter-spacing:.16em}
.cat-icon{font:800 20px ui-monospace,monospace;color:var(--acc);margin:12px 0 8px;letter-spacing:-.06em}
.cat-card.soon .cat-icon,.cat-card.later .cat-icon{color:var(--dim)}
.cat-name{font-size:18px;font-weight:800}
.cat-en{font:600 10px ui-monospace,monospace;letter-spacing:.18em;color:var(--dim);margin:2px 0 10px}
.cat-desc{font-size:12.5px;color:var(--muted);line-height:1.65;flex:1}
.cat-soon{font-size:11px;color:var(--warn);font-weight:700;margin-top:12px;letter-spacing:.1em}
.cat-card.later .cat-soon{color:var(--dim)}
.cat-card.live .cat-soon{color:var(--acc)}

/* ---------- 分类页 ---------- */
.crumb{font-size:13px;color:var(--dim);padding:22px 0 0;display:flex;gap:8px;flex-wrap:wrap}
.crumb a{color:var(--muted)} .crumb a:hover{color:var(--acc)} .crumb b{color:var(--txt);font-weight:600}
.cat-hero{padding:34px 0 10px}
.cat-hero .big{font-size:clamp(34px,5vw,58px);font-weight:850;letter-spacing:-.045em;margin:14px 0 12px}
.cat-hero .lead{color:var(--muted);font-size:16px;max-width:760px;margin:0 0 20px}
.kpi{display:flex;gap:10px;flex-wrap:wrap;margin-top:22px}
.kpi div{padding:12px 18px;border:1px solid var(--line);border-radius:12px;background:var(--surface)}
.kpi b{font:800 20px ui-monospace,monospace;color:var(--acc);margin-right:7px}
.kpi span{font-size:12px;color:var(--dim)}
.theme-row{display:flex;gap:9px;flex-wrap:wrap;align-items:center;margin:0 0 20px}
.theme-row .lbl{font-size:13px;color:var(--dim);margin-right:4px}
.subj-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:14px}
.subj-card{padding:22px;border-radius:16px;border:1px solid var(--line);background:var(--surface);
  transition:.24s;position:relative;overflow:hidden;display:flex;flex-direction:column;min-height:210px}
.subj-card::before{content:"";position:absolute;left:0;top:0;bottom:0;width:3px;background:var(--sacc,var(--acc));opacity:.8}
.subj-card:hover{transform:translateY(-5px);border-color:var(--line2);background:var(--surface2)}
.subj-card.off{opacity:.55}
.subj-icon{font:800 15px ui-monospace,monospace;letter-spacing:-.04em;color:var(--sacc,var(--acc));
  display:inline-block;padding:5px 10px;border-radius:8px;background:color-mix(in srgb,var(--sacc,var(--acc)) 12%,transparent);align-self:flex-start}
.subj-name{font-size:19px;font-weight:800;margin:12px 0 6px}
.subj-desc{font-size:13px;color:var(--muted);line-height:1.7;flex:1}
.subj-meta{display:flex;justify-content:space-between;font-size:12px;color:var(--dim);margin-top:14px;
  padding-top:12px;border-top:1px solid var(--line)}
.mini-bar{height:4px;border-radius:99px;background:rgba(255,255,255,.08);margin-top:8px;overflow:hidden}
.mini-bar i{display:block;height:100%;width:0;background:var(--sacc,var(--acc));border-radius:99px}
.preview-box{margin-top:18px;border:1px dashed var(--line2);border-radius:14px;padding:18px 20px;
  background:rgba(255,255,255,.025)}
.preview-box .pl{font-size:12px;color:var(--dim);letter-spacing:.14em;margin-bottom:10px}
.preview-box .pv{font-size:15px;color:var(--txt)}
.preview-box .pv b{color:var(--acc)}
.q-list{display:grid;gap:10px}
.q-item{display:flex;align-items:center;gap:14px;padding:14px 18px;border:1px solid var(--line);
  border-radius:12px;background:var(--surface);transition:.2s}
.q-item:hover{border-color:color-mix(in srgb,var(--acc) 40%,transparent);transform:translateX(4px);background:var(--surface2)}
.q-item .n{font:800 12px ui-monospace,monospace;color:var(--acc);min-width:38px}
.q-item .t{flex:1;font-size:14.5px;line-height:1.6}
.q-item .tp{font-size:11px;color:var(--dim);border:1px solid var(--line);padding:3px 8px;border-radius:6px;white-space:nowrap}
.other-cats{display:grid;grid-template-columns:repeat(3,1fr);gap:10px}
.other-cat{display:flex;gap:12px;align-items:center;padding:14px 16px;border:1px solid var(--line);
  border-radius:12px;background:var(--surface)}
.other-cat i{font:800 13px ui-monospace,monospace;color:var(--dim);font-style:normal;min-width:26px}
.other-cat b{font-size:14px;display:block}
.other-cat span{font-size:11.5px;color:var(--dim)}

/* ---------- 内容页（长文精讲） ---------- */
.read-progress{position:fixed;top:0;left:0;height:3px;width:0;z-index:60;
  background:linear-gradient(90deg,var(--acc),var(--ac2));box-shadow:0 0 12px var(--acc)}
.article-layout{display:grid;grid-template-columns:220px minmax(0,1fr);gap:44px;padding:44px 0 20px}
.toc{position:sticky;top:96px;align-self:start;font-size:13.5px}
.toc .tt{font-size:11px;letter-spacing:.2em;color:var(--dim);font-weight:700;margin-bottom:14px}
.toc a{display:block;padding:7px 0 7px 14px;border-left:2px solid var(--line);color:var(--muted);transition:.2s}
.toc a:hover,.toc a.on{color:var(--acc);border-color:var(--acc);background:linear-gradient(90deg,color-mix(in srgb,var(--acc) 8%,transparent),transparent)}
.article{min-width:0}
.article .a-meta{display:flex;gap:8px;flex-wrap:wrap;margin-bottom:18px}
.article h1{font-size:clamp(25px,3.5vw,38px);font-weight:820;letter-spacing:-.03em;line-height:1.42;margin:0 0 18px}
.article .a-lead{color:var(--muted);font-size:16px;border-left:3px solid var(--acc);padding-left:18px;margin:0 0 34px}
.article h2{font-size:22px;font-weight:800;margin:44px 0 14px;display:flex;align-items:center;gap:11px;scroll-margin-top:96px}
.article h2::before{content:"";width:5px;height:20px;border-radius:3px;background:linear-gradient(var(--acc),var(--ac2))}
.article p{color:#c8d2e8;font-size:15.5px;line-height:1.95;margin:0 0 16px}
.article strong{color:var(--txt)}
.q-recap{padding:22px;border-radius:16px;border:1px solid var(--line2);background:var(--surface);margin-bottom:12px}
.q-recap .opts .opt{cursor:default;pointer-events:none}
.answer-card{padding:22px;border-radius:16px;border:1px solid color-mix(in srgb,var(--ok) 42%,transparent);
  background:linear-gradient(140deg,color-mix(in srgb,var(--ok) 12%,transparent),var(--surface));margin:22px 0}
.answer-card .lab{font-size:12px;letter-spacing:.16em;color:var(--ok);font-weight:800}
.answer-card .val{font-size:24px;font-weight:850;margin:6px 0 8px}
.answer-card .sub{font-size:14px;color:var(--muted)}
.callout{padding:18px 20px;border-radius:14px;border:1px solid var(--line);background:var(--surface);margin:18px 0}
.callout.warn{border-color:color-mix(in srgb,var(--warn) 35%,transparent);background:color-mix(in srgb,var(--warn) 6%,transparent)}
.callout .ct{font-size:12px;letter-spacing:.14em;font-weight:800;color:var(--warn);margin-bottom:8px}
.copybox{position:relative;border:1px solid var(--line2);border-radius:13px;background:#080d1c;margin:14px 0 0}
.copybox pre{margin:0;padding:20px 58px 20px 20px;overflow:auto;
  font:13px/1.9 ui-monospace,SFMono-Regular,Consolas,monospace;color:#b9c8e8;white-space:pre-wrap}
.copybtn{position:absolute;right:10px;top:10px;padding:6px 11px;font-size:12px;border-radius:8px;
  border:1px solid var(--line2);background:rgba(255,255,255,.06);color:var(--muted);transition:.2s}
.copybtn:hover{color:var(--acc);border-color:var(--acc)}
.tag-row{display:flex;gap:8px;flex-wrap:wrap;margin:26px 0 0}
.rel-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:12px;margin-top:16px}
.rel-grid a{padding:16px;border:1px solid var(--line);border-radius:12px;background:var(--surface);
  font-size:13.5px;line-height:1.6;transition:.2s}
.rel-grid a:hover{border-color:color-mix(in srgb,var(--acc) 45%,transparent);transform:translateY(-3px);background:var(--surface2)}
.rel-grid a span{display:block;color:var(--dim);font-size:11px;margin-top:6px}
.pager{display:grid;grid-template-columns:1fr 1fr;gap:12px;margin:44px 0 0}
.pager a{padding:18px 20px;border:1px solid var(--line);border-radius:14px;background:var(--surface);transition:.2s}
.pager a:hover{border-color:color-mix(in srgb,var(--acc) 45%,transparent);transform:translateY(-3px)}
.pager small{display:block;color:var(--dim);font-size:11px;letter-spacing:.14em;margin-bottom:6px}
.pager b{font-size:14px;line-height:1.6;font-weight:650}
.pager .next{text-align:right}
.reanswer{margin-top:22px;padding:20px;border:1px dashed var(--line2);border-radius:14px;background:rgba(255,255,255,.02)}
.reanswer .rl{font-size:12px;color:var(--dim);letter-spacing:.14em;margin-bottom:12px}

/* ---------- 页脚 ---------- */
.footer{margin-top:76px;border-top:1px solid var(--line);padding:34px 0 46px;background:rgba(0,0,0,.18)}
.footer .fg{display:grid;grid-template-columns:1.4fr 1fr 1fr;gap:30px}
.footer h4{font-size:13px;letter-spacing:.14em;color:var(--dim);margin:0 0 12px;font-weight:700}
.footer p,.footer a{font-size:13px;color:var(--muted);line-height:2}
.footer a:hover{color:var(--acc)}
.footer .fl{display:flex;flex-direction:column}
.footer .copy{margin-top:26px;padding-top:18px;border-top:1px solid var(--line);font-size:12px;color:var(--dim)}

/* ---------- 入场动效（纯 CSS + IO，一次触发） ---------- */
.reveal{opacity:0;transform:translateY(20px);transition:opacity .6s ease,transform .6s cubic-bezier(.2,.8,.2,1)}
.reveal.in{opacity:1;transform:none}
.reveal.d1{transition-delay:.07s}.reveal.d2{transition-delay:.14s}.reveal.d3{transition-delay:.21s}

/* ---------- 答题解析模态框（首页 / 旧滚动版共用） ---------- */
.fb-modal{position:fixed;inset:0;z-index:200;display:grid;place-items:center;
  padding:clamp(12px,3vw,32px)}
.fb-modal[hidden]{display:none}
.fb-mask{position:absolute;inset:0;background:rgba(3,6,14,.74);
  backdrop-filter:blur(6px);animation:fbfade .22s ease}
.fb-box{position:relative;width:min(520px,100%);max-height:min(86dvh,720px);overflow:auto;
  padding:clamp(20px,3vw,32px);border-radius:20px;border:1px solid var(--line2);
  background:linear-gradient(160deg,rgba(24,33,58,.98),rgba(9,14,28,.99));
  box-shadow:0 30px 90px rgba(0,0,0,.7);
  animation:fbpop .26s cubic-bezier(.2,.8,.2,1)}
.fb-box::before{content:"";position:absolute;top:0;left:0;right:0;height:2px;border-radius:20px 20px 0 0;
  background:linear-gradient(90deg,transparent,var(--acc),var(--ac2),transparent)}
.fb-x{position:absolute;right:14px;top:12px;width:30px;height:30px;border-radius:9px;
  border:1px solid var(--line2);background:var(--surface);color:var(--muted);
  font-size:19px;line-height:1;display:grid;place-items:center;transition:.2s}
.fb-x:hover{color:var(--txt);border-color:var(--acc)}
.fb-badge{font-size:clamp(20px,2.4vw,26px);font-weight:850;letter-spacing:-.02em;
  margin-bottom:8px;padding-right:36px}
.fb-badge.ok{color:var(--ok)} .fb-badge.no{color:var(--no)}
.fb-ans{font-size:14px;color:var(--muted);margin-bottom:16px}
.fb-ans b{font:800 20px ui-monospace,SFMono-Regular,Consolas,monospace;
  color:var(--acc);margin-left:6px}
/* 错题回炉提示：主屏会话答题时显示，其余页面保持隐藏 */
.fb-loop{margin:0 0 14px;padding:9px 12px;border-radius:10px;
  font-size:12.5px;line-height:1.6;border:1px solid var(--line2);
  background:rgba(255,255,255,.045)}
.fb-loop[hidden]{display:none}
.fb-loop.ok{color:var(--ok);border-color:color-mix(in srgb,var(--ok) 40%,transparent);
  background:color-mix(in srgb,var(--ok) 8%,transparent)}
.fb-loop.no{color:var(--warn);border-color:color-mix(in srgb,var(--warn) 40%,transparent);
  background:color-mix(in srgb,var(--warn) 8%,transparent)}
.fb-sec{margin-top:14px;padding-top:14px;border-top:1px solid var(--line)}
.fb-sec>span{display:block;font-size:11px;letter-spacing:.18em;color:var(--dim);
  font-weight:700;margin-bottom:8px}
.fb-sec p{margin:0;color:#c8d2e8;font-size:14px;line-height:1.85}
.fb-acts{display:flex;gap:10px;justify-content:flex-end;margin-top:22px;flex-wrap:wrap}
@keyframes fbfade{from{opacity:0}to{opacity:1}}
@keyframes fbpop{from{opacity:0;transform:translateY(14px) scale(.97)}to{opacity:1;transform:none}}

/* ---------- 响应式 ---------- */
@media (max-width:980px){
  .hero-grid{grid-template-columns:1fr;gap:28px}
  .hero-visual{min-height:420px}
  .cat-grid{grid-template-columns:repeat(2,1fr)}
  .roam-grid{grid-template-columns:repeat(3,1fr)}
  .subj-grid,.rel-grid,.other-cats{grid-template-columns:repeat(2,1fr)}
  .article-layout{grid-template-columns:1fr;gap:0}
  .toc{display:none}
}
@media (max-width:640px){
  .wrap{padding:0 16px}
  /* 移动端杜绝横向溢出：裁掉任何超出视口的装饰/内容，并允许 flex/grid 子项收缩换行 */
  html,body{overflow-x:hidden}
  .bg-fx .orb{display:none}
  .opt,.opt .txt,.article,.q-recap,.opts{min-width:0}
  .opts{grid-template-columns:1fr}
  .opt{font-size:14.5px;padding:13px 14px;gap:11px}
  .opt .key{flex:0 0 26px;height:26px}
  .sec{padding:56px 0 4px}
  .topbar .wrap{height:60px;gap:12px}
  .brand span{display:none}
  .nav{gap:0}
  .nav a{padding:6px 9px;font-size:13px}
  .top-cta .btn.ghost{display:none}
  .hero{padding:46px 0 30px}
  .quiz-card{padding:20px}
  .cat-grid,.roam-grid,.subj-grid,.rel-grid,.other-cats,.pager{grid-template-columns:1fr}
  .pager .next{text-align:left}
  /* 移动端页脚：品牌块整行置顶，两个链接列并排；链接做成带分隔线的行，避免稀疏堆叠 */
  .footer{margin-top:46px;padding:28px 0 34px}
  .footer .fg{grid-template-columns:1fr 1fr;gap:18px 24px;align-items:start}
  .footer .fg>div:first-child{grid-column:1 / -1;margin-bottom:2px}
  .footer .fg>div:first-child p{margin:0;font-size:12.5px;line-height:1.65;max-width:48ch}
  .footer h4{margin-bottom:9px}
  .footer p,.footer a{font-size:12.5px;line-height:1.7}
  .footer .fl a{display:block;padding:5px 0}
  .footer .fl a:hover{padding-left:4px}
  .footer .copy{margin-top:20px;padding-top:14px;line-height:1.6;font-size:11.5px}
  .article h1{font-size:25px}
  .fb-modal{padding:12px}
  .fb-box{padding:18px;max-height:88dvh;border-radius:16px}
  .fb-sec p{font-size:13px;line-height:1.75}
  .fb-acts{gap:8px;margin-top:16px}
  .fb-acts .btn{flex:1;padding:9px 12px;font-size:13px}
}
@media (max-height:620px){
  .fb-box{max-height:92dvh;padding:16px 20px}
  .fb-sec{margin-top:10px;padding-top:10px}
  .fb-acts{margin-top:14px}
}
@media (prefers-reduced-motion:reduce){
  *,*::before,*::after{animation-duration:.01ms!important;animation-iteration-count:1!important;
    transition-duration:.01ms!important;scroll-behavior:auto!important}
  .reveal{opacity:1;transform:none}
}