:root{
  --ink:#2C2A29; --ink-2:#4A4644; --muted:#7A726C;
  --accent:#D9622B; --accent-d:#B94E1F; --accent-l:#FBE7DB;
  --cream:#FBF6EE; --paper:#F6F1E9; --line:#E8DFD3; --white:#fff;
  --ok:#2F8A57; --ok-l:#E3F3EA; --bad:#C2412D; --bad-l:#FBE5E0;
  --phy:#D9622B; --chem:#3D7A8A; --chem-l:#E1EEF1;
  --r:16px; --r-s:10px;
  --sh:0 1px 2px rgba(44,42,41,.06),0 6px 20px rgba(44,42,41,.08);
  --sh-h:0 2px 4px rgba(44,42,41,.08),0 12px 30px rgba(44,42,41,.14);
  --font:"PingFang SC","Microsoft YaHei","Hiragino Sans GB","Noto Sans CJK SC","Source Han Sans SC",system-ui,-apple-system,"Segoe UI",sans-serif;
  --maxw:1080px;
}
*{box-sizing:border-box}
html{font-size:16px;-webkit-text-size-adjust:100%}
html.proj{font-size:20px}
body{margin:0;font-family:var(--font);color:var(--ink);background:var(--paper);line-height:1.65;padding-bottom:76px}
@media(min-width:900px){body{padding-bottom:0}}
a{color:var(--accent-d)}
b,strong{font-weight:700}
sub,sup{font-size:.72em}
button{font-family:inherit;font-size:inherit}
:focus-visible{outline:3px solid var(--accent);outline-offset:2px;border-radius:6px}
.sr{position:absolute;width:1px;height:1px;overflow:hidden;clip:rect(0 0 0 0);white-space:nowrap}
.skip{position:absolute;left:-999px;top:8px;background:var(--ink);color:#fff;padding:8px 14px;border-radius:8px;z-index:99}
.skip:focus{left:8px}

/* top bar */
.topbar{position:sticky;top:0;z-index:20;background:rgba(44,42,41,.97);color:var(--cream);backdrop-filter:saturate(1.4) blur(8px)}
.topbar-inner{max-width:var(--maxw);margin:0 auto;display:flex;align-items:center;gap:16px;padding:10px 16px}
.brand{display:flex;align-items:center;gap:10px;color:inherit;text-decoration:none;margin-right:auto}
.brand-mark{display:grid;place-items:center;width:40px;height:40px;border-radius:12px;background:var(--accent);color:#fff;font-weight:800;font-size:14px;letter-spacing:1px}
.brand-text{display:flex;flex-direction:column;line-height:1.2}
.brand-text b{font-size:16px}.brand-text small{font-size:12px;opacity:.7}
.mainnav{display:none;gap:4px}
.mainnav a{color:#E9E1D6;text-decoration:none;padding:8px 12px;border-radius:999px;font-size:15px;transition:background .2s,color .2s}
.mainnav a:hover{background:rgba(255,255,255,.08)}
.mainnav a.on{background:var(--accent);color:#fff}
@media(min-width:900px){.mainnav{display:flex}}
.icon-btn{background:rgba(255,255,255,.1);border:0;color:var(--cream);width:40px;height:40px;border-radius:12px;cursor:pointer;font-size:18px}
.icon-btn[aria-pressed=true]{background:var(--accent);color:#fff}

/* bottom tab bar (mobile) */
.tabbar{position:fixed;bottom:0;left:0;right:0;z-index:20;display:flex;background:var(--white);border-top:1px solid var(--line);padding-bottom:env(safe-area-inset-bottom);box-shadow:0 -4px 16px rgba(44,42,41,.06)}
.tabbar a{flex:1;display:flex;flex-direction:column;align-items:center;gap:2px;padding:8px 0 9px;font-size:12px;color:var(--muted);text-decoration:none;min-height:58px;justify-content:center}
.tabbar a span{font-size:19px;line-height:1}
.tabbar a.on{color:var(--accent);font-weight:700}
@media(min-width:900px){.tabbar{display:none}}

main{outline:none}
.view{max-width:var(--maxw);margin:0 auto;padding:20px 16px 40px;animation:fadein .28s ease}
@keyframes fadein{from{opacity:0;transform:translateY(6px)}to{opacity:1;transform:none}}
@media (prefers-reduced-motion:reduce){*{animation:none!important;transition:none!important}}

h1,h2,h3,h4{line-height:1.3;margin:0 0 .5em}
h1{font-size:1.65rem;letter-spacing:.5px}
h2{font-size:1.3rem}
h3{font-size:1.1rem}
p{margin:.4em 0}
.lead{color:var(--ink-2);font-size:1.02rem}
.muted{color:var(--muted)}
.small{font-size:.86rem}
.eyebrow{display:inline-block;font-size:.78rem;font-weight:700;letter-spacing:2px;color:var(--accent);text-transform:uppercase;margin-bottom:6px}
.page-head{margin:4px 0 18px}
.page-head h1 .hl{color:var(--accent)}
.crumbs{font-size:.88rem;margin-bottom:8px}
.crumbs a{text-decoration:none}

.card{background:var(--white);border-radius:var(--r);box-shadow:var(--sh);padding:18px;border:1px solid rgba(232,223,211,.7)}
.card.cream{background:var(--cream)}
.card.dark{background:var(--ink);color:var(--cream);border-color:var(--ink)}
.card.dark .muted{color:#BFB5AA}
.grid{display:grid;gap:14px}
.g2{grid-template-columns:1fr}
.g3{grid-template-columns:1fr}
@media(min-width:640px){.g2{grid-template-columns:1fr 1fr}.g3{grid-template-columns:1fr 1fr}}
@media(min-width:900px){.g3{grid-template-columns:repeat(3,1fr)}}
.stack>*+*{margin-top:14px}
.row{display:flex;gap:10px;flex-wrap:wrap;align-items:center}
.spacer{flex:1}

/* buttons */
.btn{display:inline-flex;align-items:center;justify-content:center;gap:6px;min-height:46px;padding:10px 18px;border-radius:12px;border:1.5px solid var(--line);background:var(--white);color:var(--ink);font-weight:600;cursor:pointer;text-decoration:none;transition:transform .12s,box-shadow .2s,background .2s,border-color .2s}
.btn:hover{box-shadow:var(--sh);border-color:#D9CDBE}
.btn:active{transform:scale(.98)}
.btn.primary{background:var(--accent);border-color:var(--accent);color:#fff}
.btn.primary:hover{background:var(--accent-d);border-color:var(--accent-d)}
.btn.dark{background:var(--ink);border-color:var(--ink);color:var(--cream)}
.btn.ghost{background:transparent}
.btn.sm{min-height:38px;padding:6px 12px;font-size:.9rem;border-radius:10px}
.btn[disabled]{opacity:.45;cursor:not-allowed;box-shadow:none}
.chip{display:inline-flex;align-items:center;gap:6px;min-height:40px;padding:6px 14px;border-radius:999px;border:1.5px solid var(--line);background:var(--white);color:var(--ink);cursor:pointer;font-weight:600;font-size:.92rem;text-decoration:none;transition:all .18s}
.chip:hover{border-color:var(--accent)}
.chip.on,.chip[aria-pressed=true]{background:var(--ink);border-color:var(--ink);color:#fff}
.tag{display:inline-block;font-size:.75rem;font-weight:700;padding:2px 9px;border-radius:999px;background:var(--accent-l);color:var(--accent-d);vertical-align:middle}
.tag.chem{background:var(--chem-l);color:var(--chem)}
.tag.dark{background:var(--ink);color:#fff}
.tag.ok{background:var(--ok-l);color:var(--ok)}
.tag.bad{background:var(--bad-l);color:var(--bad)}

/* hero */
.hero{display:grid;gap:18px;grid-template-columns:1fr;background:var(--ink);color:var(--cream);border-radius:22px;padding:22px;position:relative;overflow:hidden;box-shadow:var(--sh-h)}
.hero:after{content:"";position:absolute;right:-60px;top:-60px;width:220px;height:220px;border-radius:50%;background:radial-gradient(circle,rgba(217,98,43,.45),transparent 70%)}
.hero h1{font-size:1.75rem;margin-bottom:4px}
.hero h1 em{font-style:normal;color:#F3A06F}
.hero p{color:#D8CEC2}
@media(min-width:720px){.hero{grid-template-columns:1.4fr 1fr;padding:30px}}
.ring-wrap{display:flex;align-items:center;gap:18px;position:relative;z-index:1}
.ring{width:128px;height:128px;flex:none}
.ring .bg{stroke:rgba(255,255,255,.12)}
.ring .fg{stroke:var(--accent);transition:stroke-dashoffset .8s ease}
.ring text{fill:#fff;font-weight:800}
.stats{display:grid;grid-template-columns:1fr 1fr;gap:8px 16px;font-size:.88rem;color:#D8CEC2}
.stats b{display:block;color:#fff;font-size:1.25rem}
.quick{display:flex;gap:10px;flex-wrap:wrap;margin-top:14px;position:relative;z-index:1}
.quick .chip{background:rgba(255,255,255,.08);border-color:rgba(255,255,255,.18);color:#fff}
.quick .chip:hover{background:var(--accent);border-color:var(--accent)}

.bars{display:grid;gap:10px}
.bar-row{display:grid;grid-template-columns:92px 1fr 46px;gap:10px;align-items:center;font-size:.9rem;text-decoration:none;color:inherit;padding:4px 0}
.bar{height:10px;border-radius:99px;background:var(--line);overflow:hidden}
.bar>i{display:block;height:100%;border-radius:99px;background:var(--accent);transition:width .7s ease}
.bar.chem>i{background:var(--chem)}
.bar-row .pct{text-align:right;font-variant-numeric:tabular-nums;color:var(--muted)}

/* chapter & topic */
.ch-card{display:flex;gap:14px;align-items:flex-start;text-decoration:none;color:inherit;transition:transform .18s,box-shadow .2s}
.ch-card:hover{transform:translateY(-2px);box-shadow:var(--sh-h)}
.ch-ico{flex:none;width:52px;height:52px;border-radius:14px;display:grid;place-items:center;font-size:26px;background:var(--accent-l)}
.ch-card.chem .ch-ico{background:var(--chem-l)}
.ch-card h3{margin:2px 0 4px}
.ch-meta{display:flex;gap:8px;align-items:center;margin-top:8px;font-size:.82rem;color:var(--muted)}
.ch-meta .bar{flex:1}

.topic{border-left:5px solid var(--accent);scroll-margin-top:80px}
.topic.chem{border-left-color:var(--chem)}
.topic h3{display:flex;align-items:center;gap:8px}
.topic ul{margin:.3em 0 .6em;padding-left:1.2em}
.topic li{margin:.25em 0}
.formula-strip{display:flex;flex-wrap:wrap;gap:8px;margin:10px 0}
.formula{background:var(--ink);color:#fff;border-radius:10px;padding:7px 12px;font-size:.95rem;font-weight:600;letter-spacing:.2px}
.formula sub{color:#F3A06F}
.trap{background:var(--bad-l);border-radius:12px;padding:10px 14px;margin-top:10px}
.trap h4{color:var(--bad);font-size:.95rem;margin:0 0 4px}
.trap ul{margin:0;padding-left:1.15em}
.learned{margin-top:12px}

/* tools */
.tool-card{display:flex;flex-direction:column;gap:8px;text-decoration:none;color:inherit;transition:transform .18s,box-shadow .2s;position:relative}
.tool-card:hover{transform:translateY(-2px);box-shadow:var(--sh-h)}
.tool-card .big{font-size:30px}
.tool-card .seen{position:absolute;top:12px;right:12px}
.panel{background:var(--cream);border-radius:14px;padding:14px;border:1px solid var(--line)}
.form-grid{display:grid;grid-template-columns:repeat(2,1fr);gap:10px}
@media(min-width:640px){.form-grid{grid-template-columns:repeat(3,1fr)}}
label.fld{display:flex;flex-direction:column;gap:4px;font-size:.85rem;color:var(--ink-2);font-weight:600}
.fld input,.fld select,input.ans{font:inherit;font-size:1.05rem;padding:10px 12px;border-radius:10px;border:1.5px solid var(--line);background:#fff;color:var(--ink);min-height:46px;width:100%}
.fld input:focus,input.ans:focus,.fld select:focus{border-color:var(--accent);outline:none;box-shadow:0 0 0 3px rgba(217,98,43,.2)}
.steps{counter-reset:s;list-style:none;padding:0;margin:0}
.steps li{counter-increment:s;position:relative;padding:10px 12px 10px 48px;border-radius:12px;background:#fff;margin:8px 0;border:1px solid var(--line);animation:fadein .35s ease both}
.steps li:before{content:counter(s);position:absolute;left:12px;top:10px;width:26px;height:26px;border-radius:50%;background:var(--accent);color:#fff;font-weight:800;display:grid;place-items:center;font-size:.85rem}
.steps li.warn{background:var(--bad-l);border-color:#F2C6BC}
.steps li.warn:before{content:"!";background:var(--bad)}
.steps li.good{background:var(--ok-l);border-color:#BFE3CD}
.steps li.good:before{content:"✓";background:var(--ok)}
.stackbar{display:flex;height:34px;border-radius:10px;overflow:hidden;font-size:.8rem;font-weight:700;color:#fff;background:var(--line)}
.stackbar>div{display:flex;align-items:center;justify-content:center;transition:width .6s ease;white-space:nowrap;overflow:hidden}
.seg-tabs{display:flex;background:var(--line);border-radius:12px;padding:4px;gap:4px;flex-wrap:wrap}
.seg-tabs button{flex:1;min-height:40px;border:0;border-radius:9px;background:transparent;cursor:pointer;font-weight:600;color:var(--ink-2);padding:6px 10px}
.seg-tabs button[aria-selected=true]{background:#fff;color:var(--ink);box-shadow:var(--sh)}

.svgbox{background:#fff;border-radius:14px;border:1px solid var(--line);padding:8px;display:flex;justify-content:center}
.svgbox svg{width:100%;height:auto;max-height:440px}
.kv{display:grid;grid-template-columns:auto 1fr;gap:6px 12px;font-size:.95rem}
.kv dt{color:var(--muted)}.kv dd{margin:0;font-weight:700}
.state-on{color:var(--ok)}.state-off{color:var(--bad)}
.badge-big{display:inline-block;font-size:1.25rem;font-weight:800;padding:4px 14px;border-radius:12px;background:var(--accent);color:#fff}
.engine-panel{background:var(--ink);color:var(--cream);border-radius:14px;padding:16px}
.engine-panel .kv dt{color:#BFB5AA}.engine-panel .kv dd{color:#fff}
.dots{display:flex;gap:6px;flex-wrap:wrap;margin:10px 0}
.dots button{width:30px;height:30px;border-radius:50%;border:2px solid #6B625C;background:transparent;color:#BFB5AA;cursor:pointer;font-size:.75rem;font-weight:700}
.dots button.on{background:var(--accent);border-color:var(--accent);color:#fff}
.dots button.done{border-color:var(--accent);color:#F3A06F}

table.tbl{width:100%;border-collapse:separate;border-spacing:0;font-size:.93rem;background:#fff;border-radius:12px;overflow:hidden;border:1px solid var(--line)}
.tbl th,.tbl td{padding:10px 12px;text-align:left;vertical-align:top;border-bottom:1px solid var(--line)}
.tbl th{background:var(--ink);color:#fff;font-weight:700;position:sticky;top:0}
.tbl tr:last-child td{border-bottom:0}
.tbl td.sub{font-weight:800;white-space:nowrap}
.tbl .cover{background:var(--line);color:transparent;border-radius:6px;cursor:pointer;user-select:none;transition:all .2s}
.tbl .cover:hover{background:#DCCFBF}
.tbl-wrap{overflow-x:auto;border-radius:12px}

.check-list{list-style:none;padding:0;margin:0}
.check-list li{margin:8px 0}
.check-list label{display:flex;gap:12px;align-items:flex-start;background:#fff;border:1.5px solid var(--line);border-radius:12px;padding:12px;cursor:pointer;transition:border-color .2s,background .2s}
.check-list input{width:22px;height:22px;accent-color:var(--accent);flex:none;margin-top:2px}
.check-list label:has(input:checked){border-color:var(--accent);background:var(--accent-l)}
.result{border-radius:12px;padding:12px 14px;font-weight:600;animation:fadein .3s}
.result.ok{background:var(--ok-l);color:#1F6B41}
.result.bad{background:var(--bad-l);color:#9C2F1F}
.result.info{background:var(--cream);color:var(--ink);border:1px solid var(--line)}

.order-pool{display:flex;flex-wrap:wrap;gap:8px}
.order-pool button{min-height:46px}
.order-seq{display:flex;flex-wrap:wrap;gap:8px;min-height:56px;padding:8px;border-radius:12px;border:2px dashed var(--line);background:#fff;align-items:center}
.order-seq .chip{cursor:default}
.shake{animation:shake .35s}
@keyframes shake{25%{transform:translateX(-5px)}75%{transform:translateX(5px)}}

/* quiz */
.quiz-top{display:flex;align-items:center;gap:12px;margin-bottom:12px}
.quiz-top .bar{flex:1;height:8px}
.qcard{padding:22px}
.qmeta{display:flex;gap:6px;flex-wrap:wrap;margin-bottom:10px}
.qtext{font-size:1.12rem;font-weight:600;line-height:1.7;margin-bottom:14px}
.opts{display:grid;gap:10px}
.opt{display:flex;gap:12px;align-items:flex-start;text-align:left;width:100%;min-height:52px;padding:12px 14px;border-radius:12px;border:1.5px solid var(--line);background:#fff;cursor:pointer;font-size:1rem;color:var(--ink);transition:border-color .15s,background .15s,transform .1s}
.opt:hover:not([disabled]){border-color:var(--accent);background:#FFFBF7}
.opt .k{flex:none;width:28px;height:28px;border-radius:8px;display:grid;place-items:center;background:var(--paper);font-weight:800;font-size:.9rem}
.opt.correct{border-color:var(--ok);background:var(--ok-l)}
.opt.correct .k{background:var(--ok);color:#fff}
.opt.wrong{border-color:var(--bad);background:var(--bad-l)}
.opt.wrong .k{background:var(--bad);color:#fff}
.opt[disabled]{cursor:default}
.fill-row{display:flex;gap:10px;align-items:center;flex-wrap:wrap}
.fill-row input.ans{flex:1;min-width:160px}
.fill-row .unit{font-weight:700;color:var(--muted)}
.feedback{margin-top:16px;border-radius:14px;padding:14px 16px;animation:fadein .3s}
.feedback.ok{background:var(--ok-l)}
.feedback.bad{background:var(--bad-l)}
.feedback h4{margin:0 0 6px;font-size:1.02rem}
.feedback.ok h4{color:var(--ok)}.feedback.bad h4{color:var(--bad)}
.src{margin-top:12px;font-size:.8rem;color:var(--muted);border-top:1px dashed var(--line);padding-top:10px}
.src a{color:var(--muted)}
.quiz-actions{display:flex;gap:10px;margin-top:16px;flex-wrap:wrap}
.star{background:transparent;border:1.5px solid var(--line);border-radius:10px;min-height:46px;padding:6px 14px;cursor:pointer;font-weight:600}
.star[aria-pressed=true]{background:#FFF4CC;border-color:#E8C547}
.score-big{font-size:3rem;font-weight:800;color:var(--accent);line-height:1}

.list-q{display:flex;gap:12px;align-items:flex-start}
.list-q .qt{flex:1}
.empty{text-align:center;padding:36px 18px;color:var(--muted)}
.empty .big{font-size:42px}

.toast{position:fixed;left:50%;bottom:90px;transform:translateX(-50%) translateY(20px);background:var(--ink);color:#fff;padding:10px 18px;border-radius:999px;font-size:.92rem;opacity:0;pointer-events:none;transition:all .25s;z-index:50;max-width:90vw;text-align:center}
.toast.show{opacity:1;transform:translateX(-50%) translateY(0)}
@media(min-width:900px){.toast{bottom:28px}}

.footer{margin-top:34px;padding-top:16px;border-top:1px solid var(--line);font-size:.8rem;color:var(--muted)}
.footer a{color:var(--muted)}
.timeline{display:grid;gap:12px}
.tl{display:grid;grid-template-columns:110px 1fr;gap:12px;align-items:start}
.tl .when{background:var(--accent);color:#fff;font-weight:800;border-radius:12px;padding:10px;text-align:center}
.tl:nth-child(even) .when{background:var(--ink)}
.callout{border-left:5px solid var(--accent);background:var(--accent-l);padding:12px 14px;border-radius:0 12px 12px 0}
.split-cols{display:grid;gap:14px}
@media(min-width:760px){.split-cols{grid-template-columns:1.1fr 1fr}}
.meter-read{font-variant-numeric:tabular-nums}
@media print{.topbar,.tabbar,.quiz-actions,.btn{display:none!important}body{background:#fff}}
.ring.light .bg{stroke:#ECE3D8}
.ring.light text{fill:var(--ink)}
.card.dark .seg-tabs button{color:#E8DED2}
.card.dark .seg-tabs button[aria-selected="true"]{color:var(--ink)}