/* Theme: Black & orange · Font: Atkinson Hyperlegible (both chosen in the study-pack questions) */
:root{
  --bg:#0c0b0a;--surface:#161412;--raise:#1f1c19;--ink:#f3efe8;--muted:#a59d92;--line:#2c2824;
  --accent:#ff7a1a;--accent-ink:#130a02;--accent-soft:#2f1d0e;--good:#4cc38a;--good-soft:#11291d;--bad:#ff6565;--bad-soft:#341616;--idle:#3a352f;
  --f-display:"Space Grotesk","Helvetica Neue",Arial,sans-serif;
  --f-body:"Atkinson Hyperlegible","Segoe UI",Arial,sans-serif;
  --f-mono:"JetBrains Mono",ui-monospace,Menlo,Consolas,monospace;
  --ease:cubic-bezier(.22,.8,.24,1);
  color-scheme:dark;
}
:root[data-theme="light"]{
  --bg:#fbf8f3;--surface:#ffffff;--raise:#f4eee6;--ink:#1a1612;--muted:#6c645a;--line:#e7dfd4;
  --accent:#d45f00;--accent-ink:#ffffff;--accent-soft:#fdeedf;--good:#1d7a4b;--good-soft:#e1f3e9;--bad:#c42b2b;--bad-soft:#fbe5e3;--idle:#d8d0c5;
  color-scheme:light;
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
@media (prefers-reduced-motion:reduce){html{scroll-behavior:auto}*{animation:none!important;transition:none!important}}
body{margin:0;background:var(--bg);color:var(--ink);font-family:var(--f-body);font-size:17px;line-height:1.6;
  padding:0 max(16px,env(safe-area-inset-right,0px)) 80px max(16px,env(safe-area-inset-left,0px))}
a{color:var(--accent)}
h1,h2,h3{font-family:var(--f-display);font-weight:700;letter-spacing:-.01em;text-wrap:balance;margin:0}
mjx-container[display="true"]{overflow-x:auto;overflow-y:hidden;max-width:100%}

/* top bar shared by the three pages */
.bar{max-width:1120px;margin:0 auto;display:flex;flex-wrap:wrap;align-items:center;gap:10px 18px;padding:18px 0 14px;border-bottom:1px solid var(--line)}
.brand{font-family:var(--f-display);font-weight:700;font-size:1rem;display:flex;align-items:center;gap:8px;color:var(--ink);text-decoration:none}
.brand i{width:10px;height:10px;border-radius:2px;background:var(--accent);display:inline-block}
.tabs{display:flex;gap:4px;flex-wrap:wrap}
.tabs a{font-family:var(--f-mono);font-size:.8rem;text-decoration:none;color:var(--muted);padding:6px 10px;border-radius:6px;border:1px solid transparent}
.tabs a:hover{color:var(--ink);border-color:var(--line)}
.tabs a[aria-current="page"]{color:var(--accent-ink);background:var(--accent)}
.bar .sp{flex:1}
.btn{font:inherit;font-size:.85rem;cursor:pointer;border:1.5px solid var(--line);background:var(--surface);color:var(--ink);border-radius:8px;padding:6px 12px;transition:border-color .25s var(--ease),background .25s var(--ease)}
.btn:hover{border-color:var(--accent)}
.btn:focus-visible,a:focus-visible,button:focus-visible{outline:2px solid var(--accent);outline-offset:2px}
.btn[aria-pressed="true"]{background:var(--accent-soft);border-color:var(--accent);color:var(--accent)}
.btn.primary{background:var(--accent);border-color:var(--accent);color:var(--accent-ink);font-weight:700}
.chip{font-family:var(--f-mono);font-size:.72rem;color:var(--muted);border:1px solid var(--line);border-radius:4px;padding:2px 7px;white-space:nowrap}
.demo-note{max-width:1120px;margin:12px auto 0;font-size:.85rem;color:var(--muted)}
.demo-note b{color:var(--accent)}