/* Neuroscience Field Guide — direction B: bright, clean textbook.
   One yellow = the main action. Teal = Cell basics. Indigo = After-class review. */
:root{
  --bg:#f7f5f0; --card:#fff; --ink:#1b2733; --muted:#5f6b75; --line:#e6e0d4; --soft:#f1ede4;
  --basics:#0e9f8e; --basics-soft:#e2f5f1; --review:#5b5bd6; --review-soft:#ecebfd;
  --primary:#ffc93c; --primary-dk:#f2b416;
  --good:#16a34a; --good-soft:#e6f6ea; --bad:#dc4a3a; --bad-soft:#fdeceb; --help:#7c5cd6; --help-soft:#f0ebfd;
  --r:18px; --shadow:0 1px 2px rgba(27,39,51,.06),0 8px 24px rgba(27,39,51,.07);
  --font:"Avenir Next","Segoe UI",system-ui,-apple-system,"PingFang SC","Hiragino Sans GB","Microsoft YaHei",sans-serif;
  color-scheme:light;
}
*{box-sizing:border-box}
html{-webkit-text-size-adjust:100%}
body{margin:0;background:var(--bg);color:var(--ink);font:17px/1.55 var(--font)}
a{color:inherit}
button{font:inherit;color:inherit;cursor:pointer}
:focus-visible{outline:3px solid #2563eb;outline-offset:2px;border-radius:6px}
[hidden]{display:none!important}
.skip{position:absolute;left:-999px}.skip:focus{left:12px;top:12px;background:#fff;padding:8px 12px;z-index:9}
.muted{color:var(--muted)} .small{font-size:14.5px} .center{text-align:center}
.kicker{margin:0 0 6px;font-size:13px;font-weight:800;letter-spacing:1.4px;text-transform:uppercase;color:var(--muted)}

/* ---------- header ---------- */
.top{position:sticky;top:0;z-index:20;display:flex;align-items:center;gap:18px;padding:12px clamp(16px,3vw,36px);background:rgba(255,255,255,.92);backdrop-filter:blur(8px);-webkit-backdrop-filter:blur(8px);border-bottom:1px solid var(--line)}
.brand{font-weight:800;font-size:17px;text-decoration:none;letter-spacing:.2px;white-space:nowrap}
.mainnav{display:flex;gap:6px;flex:1;justify-content:center}
.mainnav a{text-decoration:none;font-weight:700;font-size:15.5px;padding:8px 14px;border-radius:99px;color:var(--muted)}
.mainnav a:hover{background:var(--soft);color:var(--ink)}
.mainnav a.on{background:var(--ink);color:#fff}
.mainnav a.nb-basics.on{background:var(--basics)} .mainnav a.nb-review.on{background:var(--review)}
.lang{min-height:40px;padding:0 16px;border-radius:99px;border:1.5px solid var(--line);background:#fff;font-weight:800}
.sync-pill{font-size:12px;font-weight:700;padding:5px 10px;border-radius:99px;background:#e3f6f2;color:#0b6b60;white-space:nowrap;overflow:hidden;text-overflow:ellipsis;max-width:240px}
.sync-pill::before{content:"● ";font-size:10px}
.sync-pill.offline{background:#fff4cc;color:#6b4e00}
.sync-pill.revoked,.sync-pill.none{background:#fde8e8;color:#9b1c1c;white-space:normal;max-width:none!important;border-radius:12px}
@media (max-width:760px){.sync-pill{max-width:150px}}
.lang:hover{border-color:var(--ink)}
.storage-warning{margin:0;padding:8px 16px;background:#fff4cc;color:#6b4e00;font-size:14px;text-align:center}
main{max-width:1240px;margin:0 auto;padding:clamp(18px,3vw,40px) clamp(16px,3vw,36px) 120px;outline:none}

/* ---------- buttons ---------- */
.btn{display:inline-flex;align-items:center;justify-content:center;gap:8px;min-height:46px;padding:0 20px;border-radius:14px;border:1.5px solid transparent;font-weight:800;font-size:16px;text-decoration:none;transition:transform .1s,background .15s,border-color .15s}
.btn:active{transform:translateY(1px)}
.btn.primary{background:var(--primary);color:var(--ink);box-shadow:0 2px 0 var(--primary-dk)}
.btn.primary:hover{background:#ffd35f}
.btn.ghost{background:#fff;border-color:var(--line)}
.btn.ghost:hover{border-color:var(--ink)}
.btn.big{min-height:56px;font-size:18px;padding:0 26px}
.btn.sm{min-height:40px;padding:0 14px;font-size:15px;border-radius:12px}
.btn:disabled{opacity:.45;cursor:not-allowed}
.linkbtn{background:none;border:0;padding:4px 0;color:#2563eb;font-weight:700;text-decoration:underline;text-underline-offset:3px}

/* ---------- home ---------- */
.home-hero{text-align:center;margin:8px auto 24px;max-width:760px}
.home-hero h1{font-size:clamp(32px,4.4vw,52px);line-height:1.08;margin:0 0 10px;letter-spacing:-.5px}
.lede{font-size:19px;color:var(--muted);margin:0 0 6px}
.resume{display:flex;align-items:center;justify-content:space-between;gap:16px;max-width:900px;margin:0 auto 24px;padding:14px 18px;background:#fff;border:2px solid var(--primary);border-radius:var(--r);box-shadow:var(--shadow)}
.resume-where{margin:0;font-weight:800;font-size:18px}
.doors{display:grid;grid-template-columns:1fr 1fr;gap:clamp(16px,2.4vw,28px)}
.door{position:relative;display:flex;flex-direction:column;gap:6px;background:#fff;border-radius:24px;padding:22px 24px 24px;box-shadow:var(--shadow);border-top:8px solid var(--basics)}
.door-review{border-top-color:var(--review)}
.door h2{margin:0;font-size:clamp(24px,2.6vw,32px);line-height:1.15}
.door p{margin:0}
.door .btn{margin-top:auto;align-self:flex-start}
.door-art{border-radius:16px;overflow:hidden;margin-bottom:10px;background:var(--basics-soft)}
.door-review .door-art{background:var(--review-soft)}
.door-art svg{display:block;width:100%;height:auto;max-height:190px}
.door-art .tags,.door-art .trace{display:none}
.door-steps{list-style:none;margin:10px 0 6px;padding:0;display:flex;flex-wrap:wrap;gap:8px}
.door-steps li{display:flex;align-items:center;gap:6px;font-size:14.5px;font-weight:700;color:var(--muted);background:var(--soft);border-radius:99px;padding:4px 12px 4px 4px}
.door-steps li.seen{color:var(--basics);background:var(--basics-soft)}
.dot{display:inline-grid;place-items:center;min-width:26px;height:26px;border-radius:99px;background:#fff;border:1.5px solid currentColor;font-size:13px;font-weight:900}
.lvstrip{display:grid;grid-template-columns:repeat(16,1fr);gap:4px;margin:12px 0 4px}
.lvstrip i{height:10px;border-radius:4px;background:var(--soft)}
.lvstrip i.d{background:var(--review)} .lvstrip i.n{background:var(--primary)}
.home-foot{text-align:center;margin-top:26px}

/* ---------- stepper ---------- */
.stepper{display:flex;gap:6px;margin:0 0 18px;overflow-x:auto;padding-bottom:4px}
.st{display:flex;align-items:center;gap:8px;flex:1 1 0;min-width:max-content;text-decoration:none;padding:8px 14px 8px 8px;border-radius:99px;background:#fff;border:1.5px solid var(--line);color:var(--muted);font-weight:700;font-size:15px}
.st:hover{border-color:var(--basics)}
.st.seen{color:var(--basics)}
.st.on{background:var(--basics);border-color:var(--basics);color:#fff}
.st.on .dot{background:#fff;color:var(--basics);border-color:#fff}

/* ---------- a step: picture + text side by side ---------- */
.step{display:grid;grid-template-columns:minmax(0,1.2fr) minmax(0,1fr);gap:clamp(18px,2.6vw,34px);align-items:start}
.figure{position:sticky;top:84px}
.dpanel,.film{background:#fff;border-radius:24px;box-shadow:var(--shadow);padding:18px}
.textcol h1{font-size:clamp(28px,3vw,40px);line-height:1.12;margin:0 0 10px;letter-spacing:-.3px}
.idea{font-size:19px;margin:0 0 14px}
.explore{margin:0 0 12px;padding:10px 14px;border-radius:14px;background:var(--basics-soft);font-weight:700}
.help-note{margin:0 0 12px;padding:10px 14px;border-radius:14px;background:#fff7e0;border-left:4px solid var(--primary-dk);font-size:15.5px}
.bridge{margin:16px 0 0;font-size:15px;color:var(--muted);display:flex;flex-wrap:wrap;gap:8px;align-items:center}
.lvtag{display:inline-block;padding:4px 12px;border-radius:99px;background:var(--review-soft);color:var(--review);font-weight:800;font-size:14px;text-decoration:none}
.pager{position:sticky;bottom:0;z-index:10;display:flex;align-items:center;justify-content:space-between;gap:12px;margin:28px -8px 0;padding:12px 8px;background:linear-gradient(180deg,rgba(247,245,240,0),var(--bg) 35%)}
.pager-mid{text-align:center}

/* ---------- diagrams ---------- */
.art svg{display:block;width:100%;height:auto}
.art.small svg{max-height:110px}
.art.nmj svg{max-height:44vh;margin:0 auto}
.step:has(.art.nmj) .figure{position:static}
.art.mini svg{max-height:140px}
.dg .lbl{font:700 18px var(--font);fill:#1b2733;paint-order:stroke;stroke:#fff;stroke-width:5px;stroke-linejoin:round}
.dg .lbl.sm{font-size:15px}
.dg .lbl.accent{fill:#c2410c}
.dg .lbl-2{font-weight:600;font-size:.78em;fill:#5f6b75}
.dg .lead{stroke:#1b2733;stroke-width:1.5}
.dg [data-part]{cursor:pointer}
.dg .hl{fill:#ffc93c;opacity:0;pointer-events:none;transition:opacity .25s}
.dg .hl-line,.dg .hl-thick{fill:none;stroke:#ffc93c;stroke-width:16;stroke-linecap:round}
.dg .hl-thick{stroke-width:26}
.dg .hl.on{opacity:.55;animation:hlPulse 1.4s ease-in-out infinite}
@keyframes hlPulse{0%,100%{opacity:.4}50%{opacity:.75}}
.dg .zone{fill:none;stroke:transparent;stroke-width:28;pointer-events:stroke;cursor:pointer}
.dg circle.zone{fill:transparent;pointer-events:all}
.dg .trace{fill:none;stroke:#c2410c;stroke-width:4;stroke-dasharray:8 6;opacity:0}
.dg .trace.go{opacity:1;stroke-dasharray:1400;stroke-dashoffset:1400;animation:traceGo 3.2s ease-in-out forwards}
@keyframes traceGo{to{stroke-dashoffset:0}}
.dg .fadein{animation:fadeIn .5s ease both}
@keyframes fadeIn{from{opacity:0}to{opacity:1}}
.caption{margin:12px 2px 10px;font-size:16px;min-height:2.6em}
.lbl-2h{color:var(--muted);font-size:.85em}
.chips{display:flex;flex-wrap:wrap;gap:8px}
.chip{min-height:44px;padding:6px 14px;border-radius:12px;border:1.5px solid var(--line);background:#fff;font-weight:800;font-size:15.5px}
.chip:hover{border-color:var(--basics)}
.chip[aria-pressed="true"]{background:var(--primary);border-color:var(--primary-dk)}
.term small{display:block;font-weight:600;font-size:12px;color:var(--muted)}
.note{margin:12px 2px 0;font-size:14px;color:var(--muted);font-style:italic}
.dpanel>.btn{margin-top:10px}
.overview{margin-bottom:12px;border:1px solid var(--line);border-radius:14px;padding:6px 10px}
.overview summary{cursor:pointer;font-weight:800;font-size:15px;min-height:32px;display:flex;align-items:center}
.nmj-tabs{display:grid;grid-template-columns:repeat(4,1fr);gap:6px;margin-bottom:10px}
.nmj-tabs button{min-height:42px;border-radius:12px;border:1.5px solid var(--line);background:#fff;font-weight:800;font-size:14.5px}
.nmj-tabs button.done{color:var(--basics);border-color:#bfe6de}
.nmj-tabs button[aria-selected="true"]{background:var(--basics);border-color:var(--basics);color:#fff}
.transport{display:flex;gap:8px;flex-wrap:wrap;margin-top:10px}
.nmj-title{margin:12px 2px 0;font-size:18px}
.legend{display:flex;flex-wrap:wrap;gap:14px;font-size:14px;color:var(--muted);margin-top:4px}
.lg::before{content:"";display:inline-block;width:16px;height:6px;border-radius:3px;margin-right:6px;vertical-align:middle;background:#f59e0b}
.lg-ach::before{width:10px;height:10px;border-radius:99px;background:#2563eb}
.lg-enzyme::before{content:"❮";width:auto;height:auto;background:none;color:#c2410c;font-weight:900}

/* ---------- film ---------- */
.film{border-top:8px solid #ef4444}
.film h2{margin:4px 0 2px;font-size:26px;line-height:1.2}
.film p{margin:6px 0}
.lang-note{padding:8px 12px;border-radius:12px;background:#fff4e5;border-left:4px solid #f59e0b;font-size:15px}
.film .btn{margin-top:10px}
.fallback{margin-top:16px;padding:14px 16px;border-radius:16px;background:#fff;border:1.5px dashed var(--line)}
.fallback p{margin:0 0 10px}

/* ---------- questions ---------- */
.qwrap{margin-top:8px;padding:16px;border-radius:var(--r);background:#fff;box-shadow:var(--shadow)}
.question h3{margin:0 0 12px;font-size:18px;line-height:1.35}
.choices{display:flex;flex-direction:column;gap:8px}
.choice{display:flex;gap:10px;align-items:flex-start;padding:10px 12px;border-radius:12px;border:1.5px solid var(--line);background:#fff;cursor:pointer;font-size:16px}
.choice:hover{border-color:var(--basics)}
.choice:has(input:checked){border-color:var(--basics);background:var(--basics-soft)}
.choice input{margin-top:5px;width:18px;height:18px;accent-color:var(--basics)}
.choice b{min-width:18px}
.qrow{display:flex;flex-wrap:wrap;gap:8px;align-items:center;margin-top:12px}
.qhelp{display:flex;gap:14px;margin-left:auto}
.qval{color:var(--bad);font-size:14.5px;margin:8px 0 0}
.qfb{margin-top:12px;padding:12px 14px;border-radius:14px;background:var(--help-soft);border-left:5px solid var(--help);animation:fadeIn .3s}
.qfb.good{background:var(--good-soft);border-left-color:var(--good)}
.qfb.bad{background:var(--bad-soft);border-left-color:var(--bad)}
.qfb.hint{background:#fff7e0;border-left-color:var(--primary-dk)}
.qfb p{margin:6px 0 0}
.qfb .ans{font-weight:800}
.qhist{display:flex;flex-wrap:wrap;gap:4px 16px;margin-top:8px;font-size:13.5px;color:var(--muted)}
.question textarea,.note-box textarea{width:100%;border:1.5px solid var(--line);border-radius:12px;padding:10px 12px;font:16px/1.5 var(--font);background:#fffdf8}

/* ---------- readings & notes ---------- */
.readings,.note-box{margin-top:16px;padding:12px 16px;border-radius:var(--r);background:#fff;border:1.5px solid var(--line)}
.readings summary,.note-box summary,.sources summary{cursor:pointer;font-weight:800;min-height:36px;display:flex;align-items:center}
.reading{padding:10px 0;border-top:1px solid var(--line)}
.reading:first-of-type{border-top:0}
.reading-title{font-weight:800;color:#1d4ed8;text-decoration:none}
.reading-title:hover{text-decoration:underline}
.reading p,.note-box p{margin:6px 0}
.scaffold{font-weight:700}

/* ---------- wrap-up ---------- */
.done{text-align:center;max-width:980px;margin:0 auto}
.done-badge{width:84px;height:84px;margin:6px auto 10px;border-radius:99px;display:grid;place-items:center;font-size:42px;background:var(--primary);box-shadow:0 0 0 10px #fff3cc;animation:pop .5s cubic-bezier(.2,1.5,.4,1) both}
@keyframes pop{from{transform:scale(.5);opacity:0}to{transform:none;opacity:1}}
.done h1{font-size:clamp(28px,3.4vw,42px);margin:6px 0 8px}
.recap{display:grid;grid-template-columns:repeat(3,1fr);gap:16px;margin:24px 0;text-align:left}
.recap-card{display:flex;flex-direction:column;gap:8px;padding:12px;border-radius:20px;background:#fff;box-shadow:var(--shadow);text-decoration:none}
.recap-card:hover{outline:2px solid var(--basics)}
.recap-card p{margin:0 4px 4px;font-weight:700;font-size:15.5px}
.recap-card .tags,.recap-card .trace{display:none}
.next-box{padding:20px;border-radius:22px;background:var(--review-soft);margin-bottom:24px}
.next-box h2{margin:0 0 10px;font-size:20px}
.lvtags{display:flex;flex-wrap:wrap;gap:8px;justify-content:center;margin-bottom:14px}
.lvtags .lvtag{background:#fff}
.row{display:flex;gap:10px;justify-content:center;flex-wrap:wrap}
.wonder{text-align:left;max-width:720px;margin:0 auto;padding:18px;border-radius:var(--r);background:#fff;box-shadow:var(--shadow)}

/* ---------- review ---------- */
.review-head{display:flex;justify-content:space-between;align-items:flex-end;gap:24px;flex-wrap:wrap;margin-bottom:22px}
.review-head h1{font-size:clamp(30px,3.6vw,44px);margin:0 0 8px}
.review-head .lede{max-width:640px}
.review-cta{display:flex;flex-direction:column;align-items:flex-end;gap:6px}
.review-cta .btn.primary{background:var(--review);color:#fff;box-shadow:0 2px 0 #3d3db3}
.review-cta .btn.primary:hover{background:#6c6ce0}
.levels{display:grid;grid-template-columns:repeat(auto-fill,minmax(270px,1fr));gap:14px}
.chapter{background:#fff;border-radius:20px;padding:14px;box-shadow:var(--shadow)}
.ch-name{margin:0 0 8px;font-size:13px;font-weight:900;letter-spacing:1.3px;text-transform:uppercase;color:var(--review)}
.ch-levels{display:flex;flex-direction:column;gap:6px}
.lv{display:flex;align-items:center;gap:10px;padding:8px 10px;border-radius:12px;background:var(--soft)}
.lv-n{display:grid;place-items:center;min-width:34px;height:34px;border-radius:99px;background:#fff;font-weight:900;font-size:15px}
.lv-t{display:flex;flex-direction:column;line-height:1.25;flex:1;font-size:15px}
.lv-t b{font-size:12px;color:var(--muted);font-weight:800}
.lv.done{background:var(--review-soft)} .lv.done .lv-n{background:var(--review);color:#fff}
.lv.next{background:#fff6d6;outline:2px solid var(--primary)} .lv.next .lv-n{background:var(--primary)}
.lv.locked{opacity:.6}
.lv-s{white-space:nowrap}
.tipbar{display:flex;align-items:center;justify-content:space-between;gap:12px;flex-wrap:wrap;margin:22px 0 12px;padding:12px 16px;border-radius:16px;background:var(--basics-soft);font-weight:700}

/* ---------- library ---------- */
.lib-head h1{font-size:clamp(30px,3.4vw,42px);margin:0 0 6px}
.lib-h{margin:26px 0 8px;font-size:22px}
.lib-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(300px,1fr));gap:14px}
.lib-card{padding:16px;border-radius:var(--r);background:#fff;box-shadow:var(--shadow)}
.lib-card p{margin:6px 0}
.lib-notes .question,.lib-notes .note-box{margin-top:12px;padding:16px;border-radius:var(--r);background:#fff;border:1.5px solid var(--line)}
.sources{margin-top:28px;padding:12px 16px;border-radius:var(--r);background:#fff;border:1.5px solid var(--line)}

/* ---------- responsive ---------- */
@media (max-width: 980px){
  .step{grid-template-columns:1fr}
  .figure{position:static}
  .recap{grid-template-columns:1fr}
}
@media (max-width: 760px){
  .doors{grid-template-columns:1fr}
  .top{flex-wrap:wrap;gap:8px 12px}
  .mainnav{order:3;flex-basis:100%;justify-content:flex-start;overflow-x:auto}
  .mainnav a{padding:6px 12px;font-size:14.5px}
  .brand{flex:1}
  .resume{flex-direction:column;align-items:flex-start}
  .nmj-tabs{grid-template-columns:repeat(2,1fr)}
  .pager .pager-mid{display:none}
  .qhelp{margin-left:0}
  .review-cta{align-items:flex-start}
}
@media (prefers-reduced-motion: reduce){*{animation:none!important;transition:none!important}}
.legend-row{display:flex;gap:18px;margin:0 0 10px}
.lv-s{color:var(--review);font-weight:900}

/* ---------- three doors ---------- */
.doors{grid-template-columns:repeat(3,1fr)}
.door-practice{border-top-color:#e8a317}
.door-practice .door-art{background:#fff4dc}
.mainnav a.nb-practice.on{background:#c98a0c}
@media (max-width: 1100px){.doors{grid-template-columns:1fr 1fr}.door-review{grid-column:1/-1}}
@media (max-width: 760px){.doors{grid-template-columns:1fr}}
.return-bar{position:sticky;top:64px;z-index:12;display:flex;align-items:center;justify-content:space-between;gap:12px;flex-wrap:wrap;margin:-8px 0 16px;padding:10px 14px;border-radius:14px;background:#fff4dc;border:2px solid #e8a317;font-weight:700}

/* ---------- past-paper practice ---------- */
.pr-head h1{font-size:clamp(28px,3.2vw,40px);margin:0 0 6px}
.pr-warn{padding:8px 12px;border-radius:12px;background:#fff4cc;color:#6b4e00}
.pr-status{padding:10px 14px;border-radius:14px;background:#fff;border:1.5px solid var(--line);color:var(--muted)}
.pr-import{display:flex;flex-direction:column;align-items:flex-start;gap:10px;padding:24px;border-radius:22px;background:#fff;box-shadow:var(--shadow);max-width:640px}
.pr-import input[type=file]{position:absolute;left:-9999px}
.pr-cards{display:flex;flex-direction:column;gap:12px;margin:18px 0}
.pr-card{display:flex;align-items:center;gap:16px;padding:14px 18px;border-radius:20px;background:#fff;box-shadow:var(--shadow);text-decoration:none;border-left:6px solid #e8a317}
.pr-card:hover{outline:2px solid #e8a317}
.pr-num{display:grid;place-items:center;min-width:42px;height:42px;border-radius:99px;background:#fff4dc;font-weight:900;font-size:18px}
.pr-card-body{flex:1;display:flex;flex-direction:column;gap:8px}
.pr-items{display:flex;flex-wrap:wrap;gap:8px}
.pr-chip{display:inline-flex;align-items:center;gap:6px;padding:4px 10px;border-radius:99px;background:var(--soft);font-weight:900}
.pr-chip small{font-weight:700;color:var(--muted)}
.pr-chip.own{background:var(--good-soft)} .pr-chip.help{background:var(--help-soft)} .pr-chip.miss{background:var(--bad-soft)}
.pr-go{font-size:22px;font-weight:900;color:#c98a0c}
.pr-crumbs{display:flex;align-items:center;gap:10px;margin-bottom:12px}
.pr-crumbs a{font-weight:800;text-decoration:none}
.pr-layout{display:grid;grid-template-columns:minmax(0,1fr) minmax(0,1.1fr);gap:clamp(16px,2.4vw,30px);align-items:start}
.pr-layout.single{grid-template-columns:minmax(0,760px);justify-content:center}
.pr-left{position:sticky;top:84px;padding:20px;border-radius:22px;background:#fff;box-shadow:var(--shadow)}
.pr-stem{margin:0 0 10px;font-size:17px;line-height:1.7}
.orig{display:block}
.helper{display:block;margin-top:2px;font-size:14.5px;color:var(--muted);font-style:italic}
.pr-fig{display:block;width:min(240px,100%);margin:8px auto 4px;border:1px solid var(--line);border-radius:12px;background:#fff}
figure{margin:0}
.pr-shared{margin-top:12px;padding:12px 14px;border-radius:16px;background:#fff4dc;border:1.5px solid #f0d28a}
.pr-shared-h{margin:0 0 6px;font-weight:900}
.pr-shared ul{list-style:none;margin:0;padding:0;display:grid;gap:4px}
.pr-shared li{display:flex;gap:8px;align-items:baseline;font-size:17px}
.pr-shared li .orig{display:inline}
.pr-shared li .helper{display:inline;margin-left:6px}
.rules{margin-top:12px}
.pr-right{display:flex;flex-direction:column;gap:16px}
.pr-item{padding:18px;border-radius:22px;background:#fff;box-shadow:var(--shadow);border-top:6px solid #e8a317}
.pr-item.optional{border-top-color:#cbd5e1}
.pr-item-h{display:flex;justify-content:space-between;align-items:center;gap:8px;margin-bottom:6px}
.pr-q{font-weight:900;font-size:14px;letter-spacing:.5px;color:var(--muted)}
.tag{font-size:12.5px;font-weight:900;padding:3px 10px;border-radius:99px}
.tag.core{background:#fff4dc;color:#9a6700} .tag.opt{background:var(--soft);color:var(--muted)}
.pr-prompt{font-size:18px;font-weight:700;line-height:1.6;margin:4px 0 12px}
.pr-opts{display:flex;flex-direction:column;gap:8px}
.pr-opts.letters{flex-direction:row;flex-wrap:wrap}
.pr-opt{display:flex;align-items:center;gap:12px;min-height:48px;padding:8px 14px;border-radius:14px;border:2px solid var(--line);background:#fff;text-align:left;font-size:17px}
.pr-opts.letters .pr-opt{min-width:58px;justify-content:center;font-size:20px}
.pr-opt b{font-size:18px}
.pr-opt:hover:not(:disabled){border-color:#e8a317}
.pr-opt[aria-checked="true"]{background:#ffc93c;border-color:#f2b416}
.pr-opt:disabled{cursor:default;opacity:.8}
.pr-fill,.pr-clue{width:100%;min-height:48px;padding:10px 14px;border-radius:14px;border:2px solid var(--line);font:17px var(--font);background:#fffdf8}
.pr-fill:focus,.pr-clue:focus{border-color:#e8a317;outline:none}
.pr-clue{margin-top:10px;min-height:42px;font-size:15px}
.pr-review{margin-top:12px;padding:14px 16px;border-radius:16px;border-left:6px solid var(--help);background:var(--help-soft);animation:fadeIn .3s}
.pr-review.good{border-left-color:var(--good);background:var(--good-soft)}
.pr-review.bad{border-left-color:var(--bad);background:var(--bad-soft)}
.pr-review p{margin:6px 0}
.pr-res{font-weight:900;font-size:17px}
.pr-mistake{font-weight:700;padding:8px 10px;border-radius:10px;background:#fff}
.pr-link{display:flex;flex-wrap:wrap;align-items:center;gap:10px;margin:10px 0;padding:8px 10px;border-radius:12px;background:#fff}
.pr-hist{margin:10px 0 0;padding-left:18px;font-size:13.5px;color:var(--muted)}
.pr-hist li.ok::marker{color:var(--good)} .pr-hist li.no::marker{color:var(--bad)}
.pr-teacher{margin:14px 0;padding:14px 16px;border-radius:18px;background:#fff;box-shadow:var(--shadow)}
.pr-teacher h3{margin:0 0 6px;font-size:16px}
@media (max-width: 980px){.pr-layout{grid-template-columns:1fr}.pr-left{position:static}}

/* 每节课（v2/learn）：首页最上面占满一行，图在左、文字在右 */
.door-lessons{grid-column:1/-1;display:grid;grid-template-columns:minmax(0,1fr) minmax(0,1.6fr);gap:20px;align-items:center}
.door-lessons .door-art{margin:0;background:#eef7f5}
.door-lessons .door-body{display:flex;flex-direction:column;gap:10px}
@media (max-width:720px){.door-lessons{grid-template-columns:1fr}}

/* 2026-10-03：首页三个入口——课程占一行，练习和 3D 实验室各占一半 */
.doors.three{grid-template-columns:1fr 1fr}
@media (max-width:720px){.doors.three{grid-template-columns:1fr}}