/* study.surriworks.com — shared style. Paper + ink look; solutions in a hand-written card. */
:root{
  --paper:#fbf8f1; --paper2:#f3eee2; --card:#fffdf8; --line:#e2dccd; --grid:#ece6d6;
  --ink:#24262b; --muted:#6c6a63; --dim:#9a968b;
  --blue:#2f6db5; --red:#c0392b; --green:#2e8b57; --amber:#d9801a; --violet:#7b4fb0;
  --hl:#fff1a8;
  --hand:"Kalam","Segoe Print","Comic Sans MS",cursive;
  --sans:"Inter",system-ui,-apple-system,"Segoe UI",Roboto,sans-serif;
  --mono:"JetBrains Mono",ui-monospace,Consolas,monospace;
  color-scheme:light;
}
@media (prefers-color-scheme: dark){
  :root:not([data-theme="light"]){
    --paper:#16171a; --paper2:#1d1f23; --card:#1b1d21; --line:#2e3036; --grid:#24262b;
    --ink:#e8e6df; --muted:#a3a097; --dim:#75736c;
    --blue:#6fa8ff; --red:#ff7a6b; --green:#5fd394; --amber:#ffb454; --violet:#b892ff;
    --hl:#4a4320; color-scheme:dark;
  }
}
:root[data-theme="dark"]{
  --paper:#16171a; --paper2:#1d1f23; --card:#1b1d21; --line:#2e3036; --grid:#24262b;
  --ink:#e8e6df; --muted:#a3a097; --dim:#75736c;
  --blue:#6fa8ff; --red:#ff7a6b; --green:#5fd394; --amber:#ffb454; --violet:#b892ff;
  --hl:#4a4320; color-scheme:dark;
}
*{box-sizing:border-box}
html{-webkit-text-size-adjust:100%;scroll-behavior:smooth}
body{margin:0;background:var(--paper);color:var(--ink);font:16px/1.65 var(--sans)}
a{color:var(--blue)}
.wrap{max-width:880px;margin:0 auto;padding:0 16px}

/* header + problem index */
header.top{position:sticky;top:0;z-index:10;background:color-mix(in srgb,var(--paper) 90%,transparent);
  backdrop-filter:blur(6px);border-bottom:1px solid var(--line)}
header.top .wrap{display:flex;align-items:center;gap:14px;height:56px;max-width:none;padding:0 18px}
.brand{font:600 14px var(--mono);color:var(--ink);text-decoration:none;white-space:nowrap}
.brand span{color:var(--green)}
.jump{display:flex;gap:4px;overflow-x:auto;scrollbar-width:none;flex:1}
.jump::-webkit-scrollbar{display:none}
.jump a{font:500 13px var(--mono);color:var(--muted);text-decoration:none;padding:4px 8px;border-radius:6px;white-space:nowrap}
.jump a:hover,.jump a.on{background:var(--paper2);color:var(--ink)}

.hero{padding:48px 0 12px}
.eyebrow{font:500 12px var(--mono);letter-spacing:.08em;text-transform:uppercase;color:var(--green)}
h1{font-size:clamp(30px,5.5vw,44px);line-height:1.1;margin:8px 0 12px;letter-spacing:-.02em}
.lede{font-size:18px;color:var(--muted);max-width:680px}

/* one problem = one section */
section.prob{padding:40px 0 8px;border-top:1px dashed var(--line);margin-top:28px;scroll-margin-top:64px}
.pnum{font:600 13px var(--mono);color:var(--muted)}
section.prob h2{font-size:26px;margin:2px 0 10px;letter-spacing:-.01em}
h3{font-size:17px;margin:22px 0 6px}
p{margin:0 0 12px}
.task{color:var(--muted);font-size:15px;border-left:3px solid var(--line);padding:2px 0 2px 12px;margin:0 0 16px}

/* formula card with the book reference */
.formula{background:var(--card);border:1px solid var(--line);border-radius:10px;padding:12px 16px;margin:12px 0;overflow-x:auto}
.formula .ref{display:block;font:500 12px var(--mono);color:var(--dim);margin-top:4px}

/* animation stage */
.stage{background:var(--card);border:1px solid var(--line);border-radius:12px;padding:10px;margin:14px 0}
.stage canvas{display:block;width:100%;touch-action:none}
.stage .cap{font-size:13px;color:var(--muted);padding:6px 4px 0}
.ctrls{display:flex;flex-wrap:wrap;align-items:center;gap:8px 14px;padding:8px 4px 2px;font-size:14px}
.ctrls button{font:500 13px var(--mono);background:var(--paper2);color:var(--ink);border:1px solid var(--line);
  border-radius:7px;padding:5px 11px;cursor:pointer}
.ctrls button:hover{border-color:var(--muted)}
.ctrls label{display:flex;align-items:center;gap:8px;color:var(--muted)}
.ctrls input[type=range]{width:140px;accent-color:var(--green)}
.ctrls output{font:500 13px var(--mono);color:var(--ink);min-width:3.5em}

/* hand-written solution sheet */
.sheet{position:relative;background:var(--card);border:1px solid var(--line);border-radius:4px 14px 6px 12px;
  padding:18px 20px 14px 46px;margin:16px 0;font:19px/1.55 var(--hand);color:var(--ink);
  background-image:linear-gradient(var(--grid) 1px,transparent 1px);background-size:100% 29.5px;background-position:0 14px;
  box-shadow:2px 3px 0 var(--line)}
.sheet::before{content:"";position:absolute;left:30px;top:0;bottom:0;border-left:2px solid color-mix(in srgb,var(--red) 45%,transparent)}
.sheet .label{font:600 12px var(--mono);letter-spacing:.08em;text-transform:uppercase;color:var(--red);display:block;margin-bottom:4px}
.sheet p{margin:0 0 8px}
.sheet .katex{font-size:1.0em}
.sheet .ans{display:inline-block;border:2px solid var(--green);border-radius:12px 5px 14px 6px;padding:1px 10px;color:var(--green);transform:rotate(-.6deg)}
.sheet mark,mark{background:var(--hl);color:inherit;padding:0 3px;border-radius:3px}
.sheet canvas{display:block;width:100%;margin:6px 0}

/* notices */
.notice{border:1px solid var(--line);border-left:4px solid var(--amber);background:var(--card);border-radius:0 10px 10px 0;
  padding:10px 14px;margin:14px 0;font-size:15px}
.notice b:first-child{color:var(--amber)}
.notice.trap{border-left-color:var(--red)}
.notice.trap b:first-child{color:var(--red)}

.tablewrap{overflow-x:auto}
table{border-collapse:collapse;font-size:14px;margin:8px 0 14px}
th,td{padding:6px 10px;border-bottom:1px solid var(--line);text-align:left}
th{font:600 12px var(--mono);color:var(--muted)}
audio{width:100%;max-width:360px;height:36px}
.audios{display:grid;grid-template-columns:repeat(auto-fit,minmax(220px,1fr));gap:8px 16px;margin:8px 0}
.audios div{font-size:13px;color:var(--muted)}

/* hub cards */
.cards{display:grid;gap:14px;margin:26px 0 60px}
.cardlink{display:block;background:var(--card);border:1px solid var(--line);border-radius:12px;padding:20px;color:var(--ink);text-decoration:none}
.cardlink:hover{border-color:var(--muted)}
.cardlink h3{margin:2px 0 6px;font-size:21px}
.cardlink p{color:var(--muted);margin:0}

footer{border-top:1px solid var(--line);margin-top:56px;padding:22px 0 40px;color:var(--dim);font-size:13px}
@media (max-width:600px){
  .sheet{padding:14px 12px 10px 30px;font-size:17px}
  .sheet::before{left:18px}
  section.prob h2{font-size:22px}
}
@media (prefers-reduced-motion: reduce){html{scroll-behavior:auto}}