html{-webkit-text-size-adjust:100%}
:root{padding-top:env(safe-area-inset-top,0px);padding-bottom:env(safe-area-inset-bottom,0px)}
body{margin:0}
img{max-width:100%}
[hidden]{display:none!important}

/* Shared look for every topic page: a science notebook on graph paper, one column of lessons.
   Color tokens: --ke orange-red (motion / push), --pe amber (stored / highlight), --tr blue (transfer / pull) */
:root{
  --paper:#f5f8fc; --grid:#e1e8f2; --ink:#1d2a44; --ink-soft:#56627a; --card:#ffffff; --line:#cdd6e5;
  --ke:#d9480f; --ke-soft:#fde8da; --pe:#c98a00; --pe-soft:#fff3cc; --tr:#1864ab; --tr-soft:#dcebfa;
  --good:#2b8a3e; --good-soft:#e0f4e5; --bad:#c92a2a; --bad-soft:#fde3e3; --hl:#f2b705;
  --f-display:"Fredoka","Noto Sans TC",system-ui,sans-serif;
  --f-en:"Atkinson Hyperlegible","Noto Sans TC",system-ui,sans-serif;
  --f-zh:"Noto Sans TC","PingFang TC","Microsoft JhengHei",system-ui,sans-serif;
}
@media (prefers-color-scheme: dark){:root:not([data-theme="light"]){
  --paper:#131a2b; --grid:#1c2540; --ink:#e9eef8; --ink-soft:#9ea9c2; --card:#1a2238; --line:#2f3a58;
  --ke:#ff8c50; --ke-soft:#3b2519; --pe:#ffcf4a; --pe-soft:#3a3115; --tr:#64b0ff; --tr-soft:#16304f;
  --good:#63d27f; --good-soft:#163823; --bad:#ff8080; --bad-soft:#3e1d1d; --hl:#ffcf4a; color-scheme:dark}}
:root[data-theme="dark"]{
  --paper:#131a2b; --grid:#1c2540; --ink:#e9eef8; --ink-soft:#9ea9c2; --card:#1a2238; --line:#2f3a58;
  --ke:#ff8c50; --ke-soft:#3b2519; --pe:#ffcf4a; --pe-soft:#3a3115; --tr:#64b0ff; --tr-soft:#16304f;
  --good:#63d27f; --good-soft:#163823; --bad:#ff8080; --bad-soft:#3e1d1d; --hl:#ffcf4a; color-scheme:dark}

*{box-sizing:border-box}
body{
  background-color:var(--paper);
  background-image:linear-gradient(var(--grid) 1px,transparent 1px),linear-gradient(90deg,var(--grid) 1px,transparent 1px);
  background-size:24px 24px;
  color:var(--ink); font-family:var(--f-en); font-size:17px; line-height:1.55;
}
.wrap{max-width:900px; margin:0 auto; padding-inline:16px; padding-block:0 64px}
h1,h2,h3{font-family:var(--f-display); text-wrap:balance; line-height:1.15; margin:0}
.zh{font-family:var(--f-zh); color:var(--ink-soft); font-size:.92em}
body.hide-zh .zh{display:none!important}
button{font:inherit; color:inherit; cursor:pointer}
button:focus-visible,input:focus-visible{outline:3px solid var(--hl); outline-offset:2px}
.c-ke{color:var(--ke)} .c-pe{color:var(--pe)} .c-tr{color:var(--tr)}

/* top bar */
.bar{position:sticky; top:env(safe-area-inset-top,0px); z-index:10; background:color-mix(in srgb,var(--paper) 92%,transparent); backdrop-filter:blur(6px); border-bottom:1px solid var(--line)}
.bar-in{max-width:900px; margin:0 auto; padding:10px 16px; display:flex; gap:10px; align-items:center; flex-wrap:wrap}
.brand{font-family:var(--f-display); font-weight:700; font-size:1.05rem; margin-right:auto}
.chips{display:flex; gap:6px; flex-wrap:wrap}
.chips a{font-size:.85rem; text-decoration:none; color:var(--ink); border:1px solid var(--line); background:var(--card); border-radius:999px; padding:3px 11px; white-space:nowrap}
.chips a:hover{border-color:var(--ink-soft)}
.toggle{display:flex; align-items:center; gap:6px; font-size:.85rem; font-family:var(--f-zh); background:var(--card); border:1px solid var(--line); border-radius:999px; padding:3px 12px 3px 6px}
.toggle input{width:18px; height:18px; accent-color:var(--tr)}
.vbtn{display:flex; align-items:center; gap:6px; font-size:.85rem; background:var(--card); border:1px solid var(--line); border-radius:999px; padding:3px 12px 3px 8px}
.vbtn svg{width:16px; height:16px; fill:var(--ink)}
.vbtn[aria-expanded="true"]{border-color:var(--ink)}
.vpanel{max-width:900px; margin:0 auto; padding:4px 16px 14px}
.vpanel-in{background:var(--card); border:1px solid var(--line); border-radius:12px; padding:14px 16px; display:grid; grid-template-columns:1fr 1fr; gap:12px 18px; align-items:end}
.vpanel label{display:grid; gap:4px; font-weight:700; font-size:.9rem; min-width:0}
.vpanel label .zh{font-weight:500}
.vpanel select{font:inherit; font-size:.95rem; padding:8px 10px; border-radius:9px; border:1px solid var(--line); background:var(--paper); color:var(--ink); width:100%; min-width:0}
.vpanel input[type=range]{width:100%; accent-color:var(--ke)}
.vrow{display:flex; gap:10px; align-items:center; flex-wrap:wrap; grid-column:1 / -1}
.vnote{grid-column:1 / -1; font-family:var(--f-zh); font-size:.88rem; color:var(--ink-soft); background:var(--pe-soft); border-radius:9px; padding:10px 12px; line-height:1.6}
.vnote b{color:var(--ink)}
.vstatus{font-size:.85rem; color:var(--ink-soft)}
@media (max-width:640px){ .vpanel-in{grid-template-columns:1fr} }

/* hero */
.hero{padding-block:36px 20px; display:grid; grid-template-columns:1.25fr .75fr; gap:24px; align-items:center}
.book{display:inline-block; font-size:.8rem; font-weight:700; letter-spacing:.06em; text-transform:uppercase; color:var(--ink-soft); border:1px solid var(--line); background:var(--card); border-radius:6px; padding:2px 8px; margin-bottom:10px}
.hero h1{font-size:clamp(2.2rem,6vw,3.3rem)}
.hero h1 .zh{display:block; font-size:.5em; margin-top:6px; font-weight:700}
.hero p{max-width:34em; margin:12px 0 0}
.thesis{font-family:var(--f-display); font-size:1.45rem; font-weight:600}
.hero-art{display:flex; justify-content:center}
.hero-art svg{width:100%; max-width:300px; height:auto}
.map{display:grid; grid-template-columns:repeat(4,1fr); gap:8px; margin-top:16px}
.map a{display:grid; gap:2px; text-decoration:none; color:var(--ink); background:var(--card); border:1px solid var(--line); border-radius:10px; padding:8px 10px; font-size:.85rem; line-height:1.3}
.map a b{font-family:var(--f-display); font-size:.95rem}
.map a:hover{border-color:var(--ink-soft)}

/* lesson sections */
section.lesson{background:var(--card); border:1px solid var(--line); border-radius:14px; padding:26px 22px; margin-top:28px; scroll-margin-top:80px}
.tag{display:inline-block; font-family:var(--f-display); font-weight:600; font-size:.8rem; letter-spacing:.08em; text-transform:uppercase; color:var(--ink-soft); margin-bottom:6px}
section.lesson h2{font-size:clamp(1.55rem,4vw,2.05rem)}
section.lesson h2 .zh{font-size:.62em; margin-left:8px; font-weight:700}
.eq{margin:8px 0 0; font-size:.95rem; color:var(--ink-soft)}
.eq b{color:var(--ink)}
.idea{margin-top:16px; background:var(--pe-soft); border-radius:10px; padding:14px 16px; display:grid; gap:10px}
.idea-label{font-family:var(--f-display); font-weight:700; font-size:.85rem; letter-spacing:.06em; text-transform:uppercase}
.line{display:flex; gap:10px; align-items:flex-start}
.line > div{min-width:0}
.line p{margin:0}
.line .en{font-weight:700}
b.kw{background:linear-gradient(transparent 60%,color-mix(in srgb,var(--hl) 45%,transparent) 60%); font-weight:700}
.say{flex:none; width:32px; height:32px; border-radius:50%; border:1px solid var(--line); background:var(--card); display:grid; place-items:center; padding:0}
.say svg{width:16px; height:16px; fill:var(--ink)}
.say:hover{border-color:var(--ink)}
.try{margin-top:20px; font-family:var(--f-display); font-weight:600; font-size:1.1rem}
.try .zh{font-weight:500; margin-left:6px}
.formula{margin-top:14px; display:flex; flex-wrap:wrap; align-items:center; gap:8px; font-family:var(--f-display); font-weight:600; font-size:1.2rem}
.formula span.box{border:2px solid var(--ink); border-radius:10px; padding:4px 12px; background:var(--card)}
.formula .zh{font-size:.8rem; display:block; font-weight:500; line-height:1.2}

/* warm-up sort */
.score{font-family:var(--f-display); font-size:1rem; margin-top:6px; color:var(--ink-soft)}
.sort{display:grid; grid-template-columns:repeat(4,1fr); gap:12px; margin-top:12px}
.item{border:2px solid var(--line); border-radius:12px; padding:12px 10px; display:flex; flex-direction:column; align-items:center; text-align:center; gap:4px; background:var(--card); transition:border-color .2s, background .2s}
.item .pic{font-size:2.2rem; line-height:1}
.item .en{font-weight:700; font-size:.95rem; line-height:1.25}
.item .zh{font-size:.82rem; line-height:1.3}
.item .btns{display:flex; flex-wrap:wrap; justify-content:center; gap:6px; margin-top:auto; padding-top:8px}
.item .btns button{border-radius:8px; padding:4px 10px; font-weight:700; font-size:.85rem; border:2px solid var(--line); background:var(--paper)}
.item.ok{border-color:var(--good); background:var(--good-soft)}
.item.no{border-color:var(--bad); background:var(--bad-soft)}
.item .fb{font-size:.8rem; line-height:1.35}
.item .fb .zh{display:block}

/* sim controls */
.controls{display:grid; grid-template-columns:repeat(2,1fr); gap:14px; margin-top:12px}
.ctrl{display:grid; gap:6px; min-width:0; align-content:start}
.ctrl .lab{font-weight:700; font-size:.95rem}
.ctrl .lab .zh{font-weight:500}
.seg{display:flex; flex-wrap:wrap; gap:6px}
.seg button{border:2px solid var(--line); background:var(--card); border-radius:9px; padding:5px 10px; font-size:.9rem; line-height:1.25; text-align:left}
.seg button[aria-pressed="true"]{border-color:var(--ink); background:var(--paper); font-weight:700}
.seg button .zh{display:block; font-size:.78rem}
.seg button:disabled{opacity:.55; cursor:default}
.stage{margin-top:16px; border:1px solid var(--line); border-radius:12px; background:var(--paper); overflow:hidden}
.stage canvas{display:block; width:100%}
.stage-note{display:flex; justify-content:space-between; gap:8px; flex-wrap:wrap; padding:6px 12px; border-top:1px solid var(--line); font-size:.78rem; color:var(--ink-soft)}
.meters{display:grid; gap:8px; margin-top:14px}
.meter{display:grid; grid-template-columns:minmax(0,190px) 1fr 64px; gap:10px; align-items:center; font-size:.9rem}
.meter .ml{font-weight:700; line-height:1.25}
.meter .ml .zh{display:block; font-weight:500; font-size:.8rem}
.meter .track{height:18px; border-radius:9px; background:color-mix(in srgb,var(--line) 55%,var(--paper)); overflow:hidden}
.meter .fill{height:100%; width:0; border-radius:9px}
.meter .mv{text-align:right; font-variant-numeric:tabular-nums; font-weight:700; font-family:var(--f-display)}
.fill.pe{background:var(--pe)} .fill.ke{background:var(--ke)} .fill.tr{background:var(--tr)}
.lab-row{display:flex; flex-wrap:wrap; gap:12px; align-items:center; margin-top:14px}
.go{font-family:var(--f-display); font-weight:700; font-size:1.1rem; border:0; border-radius:12px; padding:10px 22px; background:var(--ke); color:#fff}
.go.dark{background:var(--ink); color:var(--paper)}
.go:disabled{opacity:.5; cursor:default}
.ghost{border:1px solid var(--line); background:var(--card); border-radius:10px; padding:8px 14px; font-size:.9rem}
.result{font-family:var(--f-display); font-size:1.12rem; font-weight:600; min-width:0; flex:1 1 260px}
.result .zh{display:block; font-family:var(--f-zh); font-size:.85rem; font-weight:500}
.table-box{overflow-x:auto; margin-top:14px}
table{border-collapse:collapse; width:100%; font-size:.9rem; font-variant-numeric:tabular-nums}
th,td{border-bottom:1px solid var(--line); padding:6px 8px; text-align:left; white-space:nowrap}
th{font-size:.78rem; text-transform:uppercase; letter-spacing:.05em; color:var(--ink-soft)}
th .zh{text-transform:none; letter-spacing:0; display:block}
td.num{text-align:right; font-weight:700}
.stars{color:var(--ke); letter-spacing:1px}
.empty td{color:var(--ink-soft); font-style:italic; white-space:normal}

/* words */
.words{display:grid; grid-template-columns:repeat(auto-fill,minmax(185px,1fr)); gap:10px; margin-top:14px}
.word{border:1px solid var(--line); border-radius:12px; padding:12px; display:grid; gap:4px; background:var(--card); align-content:start}
.word-top{display:flex; justify-content:space-between; align-items:center; gap:6px}
.word .w{font-family:var(--f-display); font-size:1.2rem; font-weight:700; line-height:1.2}
.word .m{font-family:var(--f-zh); font-weight:700; font-size:1.05rem}
.word .ex{font-size:.85rem; color:var(--ink-soft)}
body.hide-zh .word .m{display:block!important; filter:blur(6px); cursor:pointer}
body.hide-zh .word .m.peek{filter:none}

/* quiz */
.quiz{display:grid; gap:14px; margin-top:14px}
.q{border:1px solid var(--line); border-radius:12px; padding:14px 16px; background:var(--card)}
.q .qt{font-weight:700}
.opts{display:flex; flex-wrap:wrap; gap:8px; margin-top:10px}
.opts button{border:2px solid var(--line); background:var(--paper); border-radius:10px; padding:6px 14px; font-weight:700}
.opts button.ok{border-color:var(--good); background:var(--good-soft)}
.opts button.no{border-color:var(--bad); background:var(--bad-soft)}
.q .why{margin-top:10px; font-size:.92rem}
.q .why .zh{display:block}
.final{font-family:var(--f-display); font-size:1.3rem; font-weight:700; margin-top:16px}

footer{margin-top:32px; color:var(--ink-soft); font-size:.85rem; text-align:center; font-family:var(--f-zh)}

@media (max-width:720px){
  .hero{grid-template-columns:1fr; padding-block:22px 8px}
  .hero-art{order:-1} .hero-art svg{max-width:220px}
  .map{grid-template-columns:repeat(2,1fr)}
  .sort{grid-template-columns:repeat(2,1fr)}
  .controls{grid-template-columns:1fr}
  .meter{grid-template-columns:minmax(0,120px) 1fr 52px; font-size:.82rem}
  section.lesson{padding:20px 14px}
  .chips{display:none}
}

/* shared additions */
.home{font-size:.85rem; text-decoration:none; color:var(--ink); font-weight:700; white-space:nowrap}
.home:hover{text-decoration:underline}
.go.small{font-size:.95rem; padding:7px 16px}
.quest{margin-top:18px; border:2px dashed var(--line); border-radius:12px; padding:12px 14px; display:flex; gap:12px; align-items:flex-start; background:var(--card)}
.quest .qi{font-size:1.8rem; line-height:1}
.quest p{margin:0}
.quest b.qn{font-family:var(--f-display); font-size:1.05rem}
@media (max-width:720px){ .home span:not(.zh){display:none} }