:root{
  --bg:#f6f7fb; --card:#fff; --ink:#1d2433; --muted:#5b6478; --line:#dfe3ee;
  --accent:#1f5fbf; --accent-soft:#e6eefb; --good:#1b8a4b; --warn:#b26a00; --bad:#c0392b;
  --c1:#1f5fbf; --c2:#d9480f; --c3:#2b9348; --c4:#7b2cbf;
  --side:300px;
}
*{box-sizing:border-box}
html,body{height:100%;margin:0}
body{font:1rem/1.55 system-ui,-apple-system,"Segoe UI",Roboto,sans-serif;color:var(--ink);background:var(--bg);display:flex;flex-direction:column}
#top{display:flex;align-items:center;gap:12px;padding:8px 14px;background:#fff;border-bottom:1px solid var(--line);flex:0 0 auto;flex-wrap:wrap}
.brand{font-weight:700;font-size:18px;color:var(--accent);white-space:nowrap}
.brand span{font-weight:400;font-size:13px;color:var(--muted);margin-left:6px}
#search{flex:1 1 220px;min-width:160px;padding:8px 12px;border:1px solid var(--line);border-radius:8px;font-size:15px}
button{font:inherit;cursor:pointer}
#menuBtn,#aboutBtn{border:1px solid var(--line);background:#fff;border-radius:8px;padding:6px 10px}
#modeSwitch{display:flex;border:1px solid var(--accent);border-radius:8px;overflow:hidden}
#modeSwitch button{border:0;background:#fff;color:var(--accent);padding:6px 14px;font-weight:600}
#modeSwitch button.on{background:var(--accent);color:#fff}
#layout{flex:1 1 auto;display:flex;min-height:0}
#side{width:var(--side);flex:0 0 var(--side);overflow:auto;background:#fff;border-right:1px solid var(--line);padding:10px 8px 40px}
#side.hide{display:none}
#main{flex:1 1 auto;overflow:auto;padding:22px clamp(14px,3vw,40px) 60px;outline:none}
.grade{font-weight:700;margin:14px 6px 4px;color:var(--muted);text-transform:uppercase;font-size:12px;letter-spacing:.06em}
details.course{margin:2px 0;border-radius:8px}
details.course>summary{cursor:pointer;padding:7px 8px;border-radius:8px;font-weight:600;list-style:none}
details.course>summary::-webkit-details-marker{display:none}
details.course>summary:hover{background:var(--accent-soft)}
details.course>summary .code{display:inline-block;min-width:58px;font-size:12px;font-weight:700;color:#fff;background:var(--accent);border-radius:5px;padding:1px 6px;margin-right:6px;text-align:center}
details.course.sci>summary .code{background:var(--c3)}
.unit{margin:6px 0 2px 14px;font-size:13px;color:var(--muted);font-weight:600}
.lnk{display:flex;gap:6px;align-items:flex-start;margin:1px 0 1px 14px;padding:5px 8px;border-radius:7px;color:var(--ink);text-decoration:none;font-size:14px;cursor:pointer}
.lnk:hover{background:var(--accent-soft)}
.lnk.cur{background:var(--accent);color:#fff}
.lnk.soon{color:#8a93a8;cursor:default}
.lnk.soon:hover{background:none}
.tick{width:16px;flex:0 0 16px;color:var(--good);font-weight:700}
.lnk.cur .tick{color:#fff}
h1{font-size:28px;margin:0 0 4px}
h2{font-size:21px;margin:26px 0 8px}
h3{font-size:17px;margin:18px 0 6px}
.crumb{font-size:13px;color:var(--muted);margin-bottom:6px}
.tag{display:inline-block;font-size:12px;border:1px solid var(--line);border-radius:999px;padding:1px 9px;margin-right:6px;color:var(--muted);background:#fff}
.card{background:var(--card);border:1px solid var(--line);border-radius:12px;padding:16px 18px;margin:14px 0}
.grid2{display:grid;grid-template-columns:minmax(0,1.15fr) minmax(0,1fr);gap:18px;align-items:start}
@media (max-width:1100px){.grid2{grid-template-columns:1fr}}
.anim{background:#fff;border:1px solid var(--line);border-radius:12px;padding:12px}
.anim canvas{width:100%;display:block;border-radius:8px;background:#fbfcff;touch-action:none}
.controls{display:grid;grid-template-columns:repeat(auto-fit,minmax(210px,1fr));gap:8px 16px;margin-top:10px}
.ctl label{display:flex;justify-content:space-between;font-size:14px;color:var(--muted)}
.ctl label b{color:var(--ink);font-variant-numeric:tabular-nums}
.ctl input[type=range]{width:100%}
.readout{margin-top:10px;padding:10px 12px;background:var(--accent-soft);border-radius:8px;font-size:15px}
.readout .k{color:var(--muted)}
.btnrow{display:flex;gap:8px;flex-wrap:wrap;margin-top:10px}
.btn{border:1px solid var(--accent);background:#fff;color:var(--accent);border-radius:8px;padding:6px 14px;font-weight:600}
.btn.fill{background:var(--accent);color:#fff}
.btn:disabled{opacity:.4;cursor:default}
.explain p{margin:.5em 0}
.explain .adv{display:none}
body.advanced .explain .adv{display:block}
body.advanced .explain .easyonly{display:none}
.callout{border-left:4px solid var(--accent);background:var(--accent-soft);padding:8px 12px;border-radius:0 8px 8px 0;margin:10px 0}
.callout.warn{border-color:var(--warn);background:#fff4e0}
.callout.good{border-color:var(--good);background:#e8f6ee}
.key{font-weight:700}
table.t{border-collapse:collapse;margin:8px 0}
table.t th,table.t td{border:1px solid var(--line);padding:4px 10px;text-align:center}
table.t th{background:var(--accent-soft)}
.q{margin:14px 0}
.q .opts{display:grid;gap:6px;margin-top:6px}
.q .opt{border:1px solid var(--line);background:#fff;border-radius:8px;padding:8px 12px;text-align:left}
.q .opt:hover{border-color:var(--accent)}
.q .opt.right{border-color:var(--good);background:#e8f6ee}
.q .opt.wrong{border-color:var(--bad);background:#fdeceb}
.q .why{display:none;margin-top:6px;font-size:14px;color:var(--muted)}
.q.done .why{display:block}
.hero{display:grid;grid-template-columns:repeat(auto-fill,minmax(250px,1fr));gap:12px}
.course-card{display:block;text-align:left;background:#fff;border:1px solid var(--line);border-radius:12px;padding:12px 14px;color:inherit}
.course-card:hover{border-color:var(--accent);box-shadow:0 2px 10px rgba(31,95,191,.12)}
.course-card .code{font-weight:700;color:var(--accent)}
.course-card.sci .code{color:var(--c3)}
.course-card small{color:var(--muted)}
.bar{height:6px;background:var(--line);border-radius:4px;margin-top:8px;overflow:hidden}
.bar i{display:block;height:100%;background:var(--good)}
.pager{display:flex;justify-content:space-between;margin-top:26px;gap:10px}
#dialog{position:fixed;inset:0;background:rgba(20,26,40,.5);display:flex;align-items:center;justify-content:center;z-index:50}
#dialog[hidden]{display:none}
#dialog .box{background:#fff;border-radius:14px;padding:20px 24px;max-width:560px;width:92%;max-height:86vh;overflow:auto}
.sr{position:absolute;left:-9999px}
.dot{display:inline-block;width:10px;height:10px;border-radius:50%;margin-right:4px;vertical-align:middle}
@media print{#top,#side,.controls,.btnrow{display:none}}

/* ---------- phone and tablet ---------- */
canvas{touch-action:pan-y}
canvas.dragzone{touch-action:none}
input[type=range]{height:34px;accent-color:var(--accent)}
.btn,.q .opt,#modeSwitch button,#menuBtn,#aboutBtn{min-height:40px}
@media (max-width:820px){
  body{font-size:16px}
  #top{gap:8px;padding:6px 8px;position:sticky;top:0;z-index:20}
  .brand span{display:none}
  #search{order:5;flex:1 1 100%}
  #modeSwitch button{padding:6px 10px}
  #side{position:fixed;top:0;bottom:0;left:0;z-index:40;width:86vw;max-width:340px;box-shadow:4px 0 24px rgba(0,0,0,.25);padding-top:14px}
  #side.hide{display:none}
  #main{padding:14px 12px 70px}
  h1{font-size:23px}
  .grid2{grid-template-columns:1fr;gap:12px}
  .controls{grid-template-columns:1fr}
  .hero{grid-template-columns:1fr 1fr}
  .pager{flex-direction:column}
  .pager .btn{text-align:center}
  .anim{padding:8px}
}
@media (max-width:420px){.hero{grid-template-columns:1fr}}
@media (pointer:coarse){.lnk{padding:10px 8px}details.course>summary{padding:11px 8px}}
#scrim{position:fixed;inset:0;background:rgba(20,26,40,.4);z-index:30}

.examBtn{border:1px solid var(--accent)!important;background:var(--accent)!important;color:#fff;border-radius:8px;padding:6px 12px;font-weight:600}
.tabs{display:flex;gap:6px;flex-wrap:wrap;margin:14px 0}
.tabs button{border:1px solid var(--line);background:#fff;border-radius:999px;padding:6px 14px;font-weight:600}
.tabs button.on{background:var(--accent);color:#fff;border-color:var(--accent)}
.pick{display:grid;grid-template-columns:repeat(auto-fill,minmax(260px,1fr));gap:4px 14px}
.pick label{display:flex;gap:8px;align-items:flex-start;padding:5px 0;cursor:pointer}
.pick input{margin-top:5px;width:18px;height:18px}
.sheet{column-count:2;column-gap:22px;font-size:14px}
.sheet .item{break-inside:avoid;border:1px solid var(--line);border-radius:8px;padding:8px 10px;margin:0 0 10px;background:#fff}
.sheet h3{margin:0 0 4px;font-size:15px}
.sheet table{width:100%;border-collapse:collapse;font-size:13px}
.sheet td{border-top:1px solid var(--line);padding:3px 4px;vertical-align:top}
.score{font-size:34px;font-weight:700;color:var(--accent)}
@media (max-width:820px){.sheet{column-count:1}.examBtn{padding:6px 8px}}
@media print{#top,#side,.noprint,#scrim{display:none!important}body{display:block;height:auto;background:#fff}#layout{display:block}#main{overflow:visible;padding:0}.sheet{column-count:2;font-size:11px}.sheet .item{border-color:#999}}
details.course.hist>summary .code{background:#b5651d}
.course-card .code{font-weight:700;color:var(--accent)}

/* Chemistry Atlas */
.ptwrap{overflow-x:auto;padding-bottom:6px}
.pt{display:grid;grid-template-columns:repeat(18,minmax(46px,1fr));gap:3px;min-width:900px}
.ptc{border:1px solid rgba(0,0,0,.18);border-radius:6px;padding:2px 1px;display:flex;flex-direction:column;align-items:center;justify-content:center;min-height:56px;cursor:pointer;font:inherit;color:var(--ink);line-height:1.1}
.ptc small{font-size:10px;color:#333;align-self:flex-start;padding-left:3px}
.ptc b{font-size:16px}
.ptc i{font-style:normal;font-size:9px;max-width:100%;overflow:hidden;text-overflow:ellipsis;white-space:nowrap;color:#333}
.ptc.on{outline:3px solid var(--accent);z-index:1}
.ptc.dim{opacity:.18}
.ptc.gap{background:#f0f0f0;cursor:default;border-style:dashed}
.ptlbl{font-size:12px;color:var(--muted);align-self:center;text-align:right;padding-right:6px}
.ptgn{font-size:11px;color:var(--muted);text-align:center}
.atlegend{display:flex;flex-wrap:wrap;gap:4px 12px;margin:8px 0;font-size:13px}
.atlegend .lg{display:inline-flex;align-items:center;gap:5px}
.atlegend i{width:14px;height:14px;border-radius:3px;border:1px solid rgba(0,0,0,.2);display:inline-block}
.elhead{display:flex;gap:14px;align-items:center;margin-bottom:8px}
.bigsym{width:84px;height:84px;border-radius:10px;display:flex;flex-direction:column;align-items:center;justify-content:center;border:1px solid rgba(0,0,0,.2)}
.bigsym b{font-size:34px;line-height:1}.bigsym small{font-size:12px}
.eltab{border-collapse:collapse;width:100%;font-size:14px}
.eltab th,.eltab td{border-bottom:1px solid var(--line);padding:5px 8px;text-align:left;vertical-align:top}
.eltab th{width:34%;color:var(--muted);font-weight:600}
.chips{display:flex;flex-wrap:wrap;gap:6px;margin:6px 0 10px}
.chip{border:1px solid var(--line);background:#fff;border-radius:999px;padding:5px 11px;font:inherit;font-size:13px;cursor:pointer}
.chip:hover{background:var(--accent-soft)}
@media(max-width:820px){.eltab th{width:42%}}

.tick.st-weak{color:#d9480f}.tick.st-started{color:var(--accent)}.lnk.cur .tick{color:#fff}

.decide .dec-text{font-size:1.05em;margin:8px 0 12px;line-height:1.5}.decide .opt{display:block;width:100%;text-align:left;margin:6px 0}
.vstrip{display:flex;gap:8px;flex-wrap:wrap;margin:8px 0}.vbtn{border:2px solid var(--line);background:var(--card,#fff);border-radius:12px;padding:8px 10px;cursor:pointer;min-width:92px;text-align:center;font:inherit;color:inherit}.vbtn.sel{border-color:var(--accent);box-shadow:0 0 0 2px var(--accent) inset}.vic{font-size:30px}.vnm{font-weight:700;font-size:.9em}
.vline{font-style:italic;background:var(--soft,#f5f2ea);border-left:4px solid var(--accent);padding:10px 12px;margin:8px 0;border-radius:6px}.btn.wrongc{background:#f8d7d2}
.srcbox{border:2px dashed #b5651d;background:#fbf4e4;border-radius:10px;padding:12px;margin:8px 0}.srctext{font-family:Georgia,serif;font-size:1.1em;margin:6px 0;text-align:center}