:root{
  --paper:#F7F9FC; --panel:#FFFFFF; --line:#D5DEEA;
  --grid:#E1E8F2; --axis:#7A889C; --ink:#1B2A44; --muted:#56637A;
  --e1:#C2332B; --e2:#1E5DBC; --fill:rgba(236,166,52,.38); --edge:#A35F08;
  --ghost:#8E99A8; --tgrid:rgba(30,93,188,.28); --ok:#227244; --okSoft:#E3F3E9; --badSoft:#FBE7E5;
  --btn:#1B2A44; --btnText:#FFFFFF; --soft:#EEF2F8; --focus:#1E5DBC;
  --ui:"Atkinson Hyperlegible", "Segoe UI", system-ui, sans-serif;
  --math:"STIX Two Text", "Cambria Math", "Times New Roman", serif;
  color-scheme:light;
}
@media (prefers-color-scheme: dark){
  :root:not([data-theme="light"]){
    --paper:#131A26; --panel:#1A2333; --line:#2D3A50;
    --grid:#222D40; --axis:#7D8BA3; --ink:#E6ECF5; --muted:#A3B0C4;
    --e1:#FF6B5E; --e2:#6FA6FF; --fill:rgba(240,176,70,.30); --edge:#F2B24F;
    --ghost:#7C889C; --tgrid:rgba(111,166,255,.30); --ok:#5FCB8A; --okSoft:#17352A; --badSoft:#3D1F22;
    --btn:#E6ECF5; --btnText:#131A26; --soft:#222D40; --focus:#6FA6FF;
    color-scheme:dark;
  }
}
:root[data-theme="dark"]{
  --paper:#131A26; --panel:#1A2333; --line:#2D3A50;
  --grid:#222D40; --axis:#7D8BA3; --ink:#E6ECF5; --muted:#A3B0C4;
  --e1:#FF6B5E; --e2:#6FA6FF; --fill:rgba(240,176,70,.30); --edge:#F2B24F;
  --ghost:#7C889C; --tgrid:rgba(111,166,255,.30); --ok:#5FCB8A; --okSoft:#17352A; --badSoft:#3D1F22;
  --btn:#E6ECF5; --btnText:#131A26; --soft:#222D40; --focus:#6FA6FF;
  color-scheme:dark;
}

*,*::before,*::after{box-sizing:border-box}
[hidden]{display:none!important}
html{-webkit-text-size-adjust:100%}
body{margin:0;background:var(--paper);color:var(--ink);font-family:var(--ui);font-size:16px;line-height:1.45;
  padding-top:env(safe-area-inset-top,0px);padding-bottom:env(safe-area-inset-bottom,0px)}
a{color:var(--e2)}
.wrap{max-width:1180px;margin:0 auto;padding:16px 16px 40px}
.math,i.v{font-family:var(--math)}
.vis{position:absolute;width:1px;height:1px;overflow:hidden;clip:rect(0 0 0 0);white-space:nowrap}

/* ---------- header ---------- */
.topbar{display:flex;flex-wrap:wrap;align-items:center;justify-content:space-between;gap:6px 16px;margin-bottom:8px}
.back{display:inline-flex;align-items:center;min-height:44px;font-weight:700;text-decoration:none;color:var(--ink)}
.back:hover{text-decoration:underline}
h1{font-family:var(--math);font-weight:600;font-size:clamp(1.5rem,3.2vw,2.2rem);margin:0 0 4px;letter-spacing:-.01em;line-height:1.2}
.lede{margin:0 0 18px;color:var(--muted);max-width:68ch}

/* ---------- two-column practice layout ---------- */
.layout{display:grid;grid-template-columns:minmax(0,1.2fr) minmax(300px,1fr);gap:20px;align-items:start}
@media (max-width:860px){.layout{grid-template-columns:minmax(0,1fr)}}
.stage{position:sticky;top:calc(env(safe-area-inset-top,0px) + 12px);background:var(--panel);border:1px solid var(--line);border-radius:14px;padding:12px}
@media (max-width:860px){.stage{position:static;padding:8px}}
.canvasbox{position:relative;width:100%;aspect-ratio:1/1;margin:0 auto}
canvas{width:100%;height:100%;display:block;touch-action:none;border-radius:8px;cursor:default}
.stagebar{display:flex;flex-wrap:wrap;gap:8px 18px;align-items:center;justify-content:space-between;margin-top:8px;font-size:.92rem;color:var(--muted)}
.stagebar label{display:flex;align-items:center;gap:8px;min-height:44px}
.hint{font-size:.88rem;color:var(--muted);margin:6px 2px 0}
.panel{display:flex;flex-direction:column;gap:14px;min-width:0}
section,.card{background:var(--panel);border:1px solid var(--line);border-radius:14px;padding:14px 16px}
section h2{font-size:1rem;margin:0 0 10px;font-weight:700}

/* ---------- score bar ---------- */
.status{display:flex;flex-wrap:wrap;gap:4px 18px;font-size:.95rem;color:var(--muted)}
.status b{color:var(--ink)}

/* ---------- controls ---------- */
button,.btn{font-family:var(--ui);font-size:1rem;font-weight:700;min-height:44px;padding:9px 16px;border-radius:9px;border:1px solid var(--btn);background:var(--btn);color:var(--btnText);cursor:pointer;text-decoration:none;display:inline-flex;align-items:center;justify-content:center;gap:6px}
button.ghost,.btn.ghost{background:transparent;color:var(--ink);border-color:var(--line)}
button:disabled{opacity:.45;cursor:not-allowed}
button:focus-visible,input:focus-visible,select:focus-visible,a:focus-visible,summary:focus-visible{outline:3px solid var(--focus);outline-offset:2px}
.row{display:flex;gap:8px;flex-wrap:wrap;align-items:center}
select,input[type=text].param{font-family:var(--ui);font-size:1rem;min-height:44px;padding:7px 8px;border:1px solid var(--line);border-radius:8px;background:var(--paper);color:var(--ink)}
select{flex:1 1 200px;min-width:0}
input.param{width:7em}
input[type=range]{accent-color:var(--e2);width:150px;min-height:44px}
input[type=checkbox],input[type=radio]{width:20px;height:20px;accent-color:var(--e2);margin:0}
.small{font-size:.88rem;color:var(--muted)}

/* ---------- matrix input ---------- */
.matrow{display:flex;align-items:center;gap:14px;flex-wrap:wrap}
.mname{font-family:var(--math);font-style:italic;font-size:1.4rem}
.matrix{display:inline-grid;grid-template-columns:repeat(2,auto);gap:6px 8px;padding:6px 12px;position:relative;font-family:var(--math)}
.matrix::before,.matrix::after{content:"";position:absolute;top:0;bottom:0;width:9px;border:2px solid var(--ink)}
.matrix::before{left:0;border-right:none}
.matrix::after{right:0;border-left:none}
.matrix input{width:5.4em;min-height:46px;font-family:var(--math);font-size:1.2rem;text-align:center;padding:6px 4px;border:1px solid var(--line);border-radius:6px;background:var(--paper);color:var(--ink)}
.matrix input.bad{border-color:var(--e1);outline:2px solid var(--e1)}
.matrix input[readonly]{opacity:.8}
@media (max-width:400px){.matrix input{width:4.6em}}

/* static bracketed matrix */
.sm{display:inline-grid;gap:2px 14px;padding:4px 10px;position:relative;text-align:center;font-family:var(--math);font-size:1.1rem;vertical-align:middle}
.sm::before,.sm::after{content:"";position:absolute;top:0;bottom:0;width:6px;border:1.5px solid var(--ink)}
.sm::before{left:0;border-right:none}.sm::after{right:0;border-left:none}
.sm span.h{font-style:italic;color:var(--muted);font-size:.8rem}

/* ---------- question text and feedback ---------- */
.question{font-size:1.15rem;margin:0 0 12px}
.desc{font-family:var(--math);font-size:1.35rem;line-height:1.3;margin:4px 0 14px;padding:10px 14px;background:var(--soft);border-radius:10px}
.feedback{border-radius:10px;padding:12px 14px;border:1px solid var(--line);background:var(--soft)}
.feedback.good{border-color:var(--ok);background:var(--okSoft)}
.feedback.bad{border-color:var(--e1);background:var(--badSoft)}
.feedback p{margin:0 0 8px}.feedback p:last-child{margin-bottom:0}
.feedback .mark{font-weight:700}
.feedback.good .mark{color:var(--ok)}
.feedback.bad .mark{color:var(--e1)}
.hintbox{margin:10px 0 0;padding:10px 12px;border-left:4px solid var(--e2);background:var(--soft);border-radius:6px}

/* ---------- multiple-choice options ---------- */
.options{display:flex;flex-direction:column;gap:8px;margin:0;padding:0;list-style:none}
.option{width:100%;justify-content:flex-start;text-align:left;font-weight:400;font-family:var(--math);font-size:1.1rem;line-height:1.3;background:var(--panel);color:var(--ink);border:2px solid var(--line);padding:10px 14px}
.option:hover:not(:disabled){border-color:var(--ink)}
.option:disabled{opacity:1;cursor:default}
.option .tag{font-family:var(--ui);font-size:.85rem;font-weight:700;margin-left:auto;padding-left:10px;white-space:nowrap}
.option.right{border-color:var(--ok);background:var(--okSoft)}
.option.right .tag{color:var(--ok)}
.option.wrong{border-color:var(--e1);background:var(--badSoft)}
.option.wrong .tag{color:var(--e1)}

/* ---------- home ---------- */
.cards{display:grid;grid-template-columns:repeat(auto-fit,minmax(240px,1fr));gap:14px;margin-top:8px}
.card{display:flex;flex-direction:column;gap:6px;text-decoration:none;color:var(--ink);transition:border-color .15s,transform .15s}
.card:hover{border-color:var(--ink)}
.card h2{font-family:var(--math);font-size:1.3rem;font-weight:600;margin:0}
.card p{margin:0;color:var(--muted)}
.card .go{margin-top:auto;padding-top:6px;font-weight:700;color:var(--e2)}
.card svg{width:56px;height:56px}

/* ---------- explore ---------- */
.checks{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:2px 12px;font-size:.95rem}
@media (max-width:420px){.checks{grid-template-columns:1fr}}
.checks label{display:flex;gap:8px;align-items:center;min-height:44px}
dl.facts{display:grid;grid-template-columns:auto 1fr;gap:6px 14px;margin:0;font-size:.95rem}
dl.facts dt{color:var(--muted)}
dl.facts dd{margin:0;font-weight:700}
.product{overflow-x:auto;padding-bottom:4px}
.eq{display:flex;align-items:center;gap:8px;font-family:var(--math);font-size:1rem;white-space:nowrap}

footer{margin-top:28px;color:var(--muted);font-size:.85rem}

@media (prefers-reduced-motion: reduce){
  *{transition:none!important;animation:none!important}
}

/* home card icons */
.i-ghost{fill:none;stroke:var(--ghost);stroke-width:2;stroke-dasharray:4 4}
.i-img{fill:var(--fill);stroke:var(--edge);stroke-width:2}
.i-e1{stroke:var(--e1);stroke-width:3}.i-e2{stroke:var(--e2);stroke-width:3}
.i-opt{fill:none;stroke:var(--muted);stroke-width:2}
.i-ok{fill:var(--okSoft);stroke:var(--ok);stroke-width:2}
.i-target{fill:none;stroke:var(--edge);stroke-width:2;stroke-dasharray:3 4}
.i-d1{fill:var(--e1)}.i-d2{fill:var(--e2)}.i-d3{fill:var(--edge)}
.i-br{fill:none;stroke:var(--ink);stroke-width:2.5}
.i-t{font-size:11px;fill:var(--ink);font-family:var(--math)}
.nw{white-space:nowrap}

/* ---------- home: ordered, lockable cards ---------- */
ol.cards{list-style:none;padding:0;margin:14px 0 0}
ol.cards>li{display:flex}
ol.cards .card{flex:1;position:relative}
.card .step{position:absolute;top:12px;right:14px;font-weight:700;font-size:.85rem;color:var(--muted);border:1px solid var(--line);border-radius:999px;min-width:26px;height:26px;display:grid;place-items:center}
.card .go{display:flex;align-items:center;gap:6px}
.card.locked{background:var(--soft);border-style:dashed;color:var(--muted);cursor:not-allowed}
.card.locked:hover{border-color:var(--line)}
.card.locked h2,.card.locked p{color:var(--muted)}
.card.locked svg:not(.lock){opacity:.35;filter:grayscale(1)}
.card.locked .go{color:var(--muted);font-weight:700}
.lock{width:18px;height:18px;flex:none;fill:currentColor;stroke:currentColor}
.badge{position:absolute;top:8px;right:48px}
.crown{width:28px;height:28px;fill:var(--gold);flex:none;vertical-align:middle}
.linkbtn{background:none;border:none;color:var(--e2);padding:0 2px;min-height:auto;font-weight:400;font-size:inherit;text-decoration:underline}
:root{--gold:#C9920A}
@media (prefers-color-scheme: dark){:root:not([data-theme="light"]){--gold:#F5C542}}
:root[data-theme="dark"]{--gold:#F5C542}

/* ---------- set progress ---------- */
.status{flex-direction:column;gap:8px}
.setline{display:flex;flex-wrap:wrap;align-items:center;gap:8px 14px}
.dots{display:flex;gap:6px;list-style:none;margin:0;padding:0}
.dots li{width:30px;height:30px;border-radius:50%;border:2px solid var(--line);display:grid;place-items:center;font-size:.85rem;font-weight:700;color:var(--muted)}
.dots li.current{border-color:var(--ink);color:var(--ink)}
.dots li.right{border-color:var(--ok);background:var(--okSoft);color:var(--ok)}
.dots li.wrong{border-color:var(--e1);background:var(--badSoft);color:var(--e1)}
.crownline{display:flex;align-items:center;gap:8px;font-size:.92rem}
.crownline .crown{width:24px;height:24px}
.crownline.earned{color:var(--ink);font-weight:700}
.qtype{margin:0 0 6px;font-size:.85rem;font-weight:700;text-transform:uppercase;letter-spacing:.06em;color:var(--e2)}
.actions{margin-top:12px}
.tip{margin:10px 0 0}
.option.selected{border-color:var(--e2);box-shadow:inset 0 0 0 1px var(--e2);background:var(--soft)}
.option.selected::before{content:"●";color:var(--e2);margin-right:8px;font-family:var(--ui)}
.summary{margin-top:12px;border-radius:10px;padding:12px 14px;border:1px solid var(--line);background:var(--panel)}
.summary.perfect{border-color:var(--gold);border-width:2px}
.summary p{margin:0 0 6px}.summary p:last-child{margin:0}
.summary .mark{display:flex;align-items:center;gap:8px;font-weight:700;font-size:1.1rem}