:root{
  --bg:#f4f7f8; --surface:#ffffff; --ink:#1b2530; --muted:#586472; --line:#e1e8ec;
  --accent:#16324f; --accent-2:#0e7c7b; --accent-ink:#fff; --teal:#0e7c7b;
  --green:#d8efe6; --green-ink:#0f6b53; --yellow:#fbf0d0; --yellow-ink:#8a6500;
  --blue:#d9e9f2; --blue-ink:#1d5a82; --red:#fbe2e0; --red-ink:#b3261e;
  --radius:16px; --shadow:0 1px 2px rgba(15,30,40,.06),0 8px 24px rgba(15,30,40,.07);
  --maxw:1080px;
}
[data-theme="dark"]{
  --bg:#0d1418; --surface:#15212a; --ink:#e6edf1; --muted:#94a3ad; --line:#243440;
  --accent:#4f9bb8; --accent-2:#2cc4b6; --accent-ink:#0d1418; --teal:#2cc4b6;
  --green:#103029; --green-ink:#6fe0bf; --yellow:#37300f; --yellow-ink:#f2cf6b;
  --blue:#102634; --blue-ink:#7fc0e8; --red:#3a1a18; --red-ink:#ff9b94;
  --shadow:0 1px 2px rgba(0,0,0,.4),0 10px 30px rgba(0,0,0,.4);
}
*{box-sizing:border-box}
html{scroll-behavior:smooth;scroll-padding-top:78px}
body{margin:0;font-family:Inter,system-ui,sans-serif;background:var(--bg);color:var(--ink);line-height:1.55;-webkit-font-smoothing:antialiased}
h1,h2,h3{line-height:1.2;margin:0 0 .4em}
a{color:var(--accent-2)} a:hover{text-decoration:underline}
.skip{position:absolute;left:-999px;top:0;background:var(--accent);color:#fff;padding:.5rem 1rem;border-radius:8px;z-index:100}
.skip:focus{left:8px;top:8px}
.muted{color:var(--muted)} .small{font-size:.85rem} .tight li{margin:.2rem 0}
.hl{background:linear-gradient(120deg,transparent 55%,rgba(14,124,123,.28) 55%);padding:0 .05em}

.topbar{position:sticky;top:0;z-index:50;display:flex;align-items:center;gap:1rem;padding:.6rem 1.2rem;background:color-mix(in srgb,var(--surface) 88%,transparent);backdrop-filter:saturate(180%) blur(10px);border-bottom:1px solid var(--line)}
.brand{display:flex;align-items:center;gap:.6rem}.brand .logo{font-size:1.45rem}
.brand strong{display:block;line-height:1.1}.brand-sub{color:var(--muted);font-size:.78rem}
.topnav{display:flex;gap:.15rem;margin-left:auto;flex-wrap:wrap}
.topnav a{padding:.35rem .6rem;border-radius:8px;color:var(--muted);font-size:.84rem;font-weight:500}
.topnav a:hover{background:var(--bg);color:var(--ink);text-decoration:none}
.topnav a.active{color:var(--accent-2);background:color-mix(in srgb,var(--accent-2) 14%,transparent)}
.topbar-actions{display:flex;align-items:center;gap:.6rem}
.icon-btn{background:var(--bg);border:1px solid var(--line);border-radius:10px;padding:.35rem .5rem;cursor:pointer;font-size:1rem}
.progress-mini{position:relative;width:38px;height:38px;display:grid;place-items:center;font-size:.62rem;font-weight:700;color:var(--accent-2)}
.ring{position:absolute;inset:0;width:38px;height:38px;transform:rotate(-90deg)}
.ring-bg{fill:none;stroke:var(--line);stroke-width:3}
.ring-fill{fill:none;stroke:var(--accent-2);stroke-width:3;stroke-linecap:round;stroke-dasharray:100 100;stroke-dashoffset:100;transition:stroke-dashoffset .5s}

.hero{padding:4rem 1.2rem 2rem;max-width:var(--maxw);margin:0 auto}
.eyebrow{text-transform:uppercase;letter-spacing:.12em;font-size:.72rem;font-weight:700;color:var(--accent-2)}
.hero h1{font-size:clamp(2rem,5vw,3.2rem);font-weight:800;letter-spacing:-.02em}
.lede{font-size:1.1rem;color:var(--muted);max-width:62ch}
.bigstat{display:grid;grid-template-columns:repeat(auto-fit,minmax(150px,1fr));gap:.8rem;margin:1.5rem 0;max-width:780px}
.bigstat .st{background:var(--surface);border:1px solid var(--line);border-radius:12px;padding:.9rem 1rem;box-shadow:var(--shadow)}
.bigstat .st b{display:block;font-size:1.5rem;color:var(--accent-2)}
.bigstat .st span{font-size:.8rem;color:var(--muted)}
.ask-card{margin:1.3rem 0;padding:1.1rem 1.3rem;background:var(--surface);border:1px solid var(--line);border-left:4px solid var(--accent-2);border-radius:12px;box-shadow:var(--shadow)}
.ask-q{display:block;color:var(--muted);font-size:.85rem;margin-bottom:.3rem}.ask-card strong{font-size:1.15rem}
.hero-cta{display:flex;gap:.8rem;flex-wrap:wrap;margin-top:1rem}
.btn{display:inline-flex;align-items:center;gap:.4rem;padding:.7rem 1.2rem;border-radius:11px;font-weight:600;font-size:.95rem;cursor:pointer;border:1px solid transparent;transition:transform .08s;font-family:inherit}
.btn:active{transform:translateY(1px)}.btn.sm{padding:.4rem .7rem;font-size:.82rem}
.btn.primary{background:var(--accent-2);color:#fff}.btn.ghost{background:var(--surface);border-color:var(--line);color:var(--ink)}
.btn.warn{background:transparent;border-color:var(--red);color:var(--red-ink)}

.band{max-width:var(--maxw);margin:0 auto;padding:2.6rem 1.2rem}
.band.alt{background:var(--surface);max-width:none;border-block:1px solid var(--line)}
.band.alt>*{max-width:var(--maxw);margin-inline:auto}
.section-head{margin-bottom:1.3rem}.section-head h2{font-size:1.55rem;font-weight:700}

.tracker{list-style:none;counter-reset:s;padding:0;margin:0 0 1.5rem;display:grid;grid-template-columns:repeat(auto-fill,minmax(190px,1fr));gap:.6rem}
.tracker li{counter-increment:s;position:relative;background:var(--surface);border:1px solid var(--line);border-radius:11px;padding:.7rem .8rem .7rem 2.5rem;cursor:pointer;font-size:.88rem;font-weight:500;box-shadow:var(--shadow)}
.tracker li::before{content:counter(s);position:absolute;left:.65rem;top:.65rem;width:1.5rem;height:1.5rem;border-radius:50%;background:var(--bg);border:1px solid var(--line);display:grid;place-items:center;font-size:.78rem;font-weight:700;color:var(--muted)}
.tracker li.done::before{content:"✓";background:var(--accent-2);color:#fff;border-color:var(--accent-2)}
.tracker li:hover{border-color:var(--accent-2)}

.card{background:var(--surface);border:1px solid var(--line);border-radius:14px;padding:1.2rem;box-shadow:var(--shadow)}
.card h3{font-size:1.05rem}
.res-grid{display:grid;grid-template-columns:1fr 1fr;gap:1rem}
@media(max-width:820px){.res-grid{grid-template-columns:1fr}}

.chap{border-top:1px dashed var(--line);padding:1.8rem 0}
.chap .badge{display:inline-block;font-size:.72rem;font-weight:700;letter-spacing:.04em;text-transform:uppercase;color:var(--accent-2);background:color-mix(in srgb,var(--accent-2) 13%,transparent);padding:.2rem .55rem;border-radius:99px}
.chap h3{font-size:1.25rem;margin:.45rem 0 .1rem}
.chap .csub{color:var(--muted);font-size:.9rem;margin-bottom:.6rem}
.chap ul{margin:.4rem 0;padding-left:1.1rem}.chap li{margin:.25rem 0;font-size:.93rem}
.chap .prompt{margin-top:.7rem;background:var(--bg);border:1px dashed var(--line);border-radius:8px;padding:.55rem .7rem;font-size:.83rem;font-family:ui-monospace,monospace;display:flex;justify-content:space-between;gap:.6rem;align-items:flex-start}
.chap .prompt button{flex:0 0 auto}
.chap .try{margin-top:.7rem;background:var(--blue);color:var(--blue-ink);border-radius:9px;padding:.6rem .8rem;font-size:.88rem}
.chap .try label{display:flex;gap:.45rem;align-items:flex-start;cursor:pointer}

.tool-grid{display:grid;grid-template-columns:1fr 1fr;gap:1rem;margin-bottom:1rem}
@media(max-width:780px){.tool-grid{grid-template-columns:1fr}}
.tool-grid label{display:block;font-weight:600;font-size:.88rem;margin:.5rem 0 .3rem}
select,.search,.builder-grid input,.builder-grid textarea{width:100%;padding:.55rem .7rem;border:1px solid var(--line);border-radius:10px;background:var(--bg);color:var(--ink);font:inherit}
select:focus,input:focus,textarea:focus{outline:2px solid var(--accent-2);outline-offset:1px}
.out{margin-top:.7rem;padding:.7rem .8rem;background:var(--bg);border:1px solid var(--line);border-radius:10px;font-size:.9rem;min-height:2.5rem}
.out.hit{background:var(--green);color:var(--green-ink);border-color:transparent}
.threev .v{display:grid;grid-template-columns:80px 1fr;gap:.5rem;padding:.4rem 0;border-bottom:1px solid var(--line);font-size:.86rem}
.threev .v b{color:var(--accent-2)}
.valblock{margin-top:0}
.tier{border:1px solid var(--line);border-radius:10px;padding:.7rem .9rem;margin:.5rem 0;background:var(--bg)}
.tier b{color:var(--accent-2)}.tier .dur{float:right;font-size:.75rem;color:var(--muted)}
.tier label{display:flex;gap:.5rem;align-items:flex-start;font-size:.86rem;margin-top:.3rem;cursor:pointer}

.builder{margin-bottom:1rem}
.builder-grid{display:grid;grid-template-columns:1fr 1fr;gap:.8rem}
@media(max-width:680px){.builder-grid{grid-template-columns:1fr}}
.builder-grid .bf label{display:block;font-weight:600;font-size:.85rem;margin-bottom:.25rem}
.builder-grid textarea{min-height:52px;resize:vertical}
.builder-out{margin-top:1rem}.bo-head{display:flex;justify-content:space-between;align-items:center;margin-bottom:.4rem}
.builder-out pre{background:var(--bg);border:1px solid var(--line);border-radius:10px;padding:.9rem;font-size:.82rem;white-space:pre-wrap;font-family:ui-monospace,monospace}

#prompts .prow{display:flex;justify-content:space-between;gap:.6rem;align-items:flex-start;padding:.5rem 0;border-bottom:1px solid var(--line);font-size:.86rem}
#prompts .prow code{font-size:.8rem;color:var(--muted)}
#prompts .prow b{display:block;color:var(--ink)}

.glossary{max-height:340px;overflow:auto;margin:.6rem 0 0}
.glossary dt{font-weight:700;font-size:.9rem;margin-top:.6rem}.glossary dd{margin:0;color:var(--muted);font-size:.86rem}

.q{background:var(--surface);border:1px solid var(--line);border-radius:12px;padding:1rem 1.1rem;margin-bottom:.8rem;box-shadow:var(--shadow)}
.q .qq{font-weight:600;margin-bottom:.5rem}
.q .opt{display:block;width:100%;text-align:left;border:1px solid var(--line);background:var(--bg);border-radius:9px;padding:.5rem .7rem;margin:.3rem 0;cursor:pointer;font:inherit;font-size:.9rem}
.q .opt:hover{border-color:var(--accent-2)}
.q .opt.correct{background:var(--green);color:var(--green-ink);border-color:transparent}
.q .opt.wrong{background:var(--red);color:var(--red-ink);border-color:transparent}
.q .explain{font-size:.85rem;color:var(--muted);margin-top:.5rem;display:none}.q.answered .explain{display:block}
.quiz-score{font-weight:700;font-size:1.05rem;text-align:center;margin-top:.6rem;color:var(--accent-2)}

/* flashcards */
.fc-wrap{max-width:660px;margin:0 auto;text-align:center}
.fc-status{margin-bottom:.6rem}
.fc-card{min-height:190px;display:grid;place-items:center;background:var(--bg);border:1px solid var(--line);border-radius:14px;padding:1.4rem;cursor:pointer;user-select:none}
.fc-face{font-size:1.08rem;font-weight:700}
.fc-face.back{font-weight:400;font-size:.95rem}
.fc-face.fc-done{font-weight:500;font-size:.95rem;color:var(--green-ink)}
.fc-hint{display:block;margin-top:.9rem;font-size:.72rem;color:var(--muted);font-weight:400;text-transform:uppercase;letter-spacing:.08em}
.fc-actions{display:flex;gap:.6rem;justify-content:center;flex-wrap:wrap;margin-top:.9rem}
.fc-foot{margin-top:.7rem;display:flex;gap:.6rem;justify-content:center}

/* exam simulator */
.exam-start{max-width:660px;margin:0 auto;text-align:center;padding:1.8rem}
.exam-stats{display:flex;gap:1.6rem;justify-content:center;flex-wrap:wrap;margin:.6rem 0 1rem;font-size:.82rem;color:var(--muted)}
.exam-stats b{display:block;color:var(--accent-2);font-size:1.35rem}
.exam-bar{position:sticky;top:64px;z-index:40;display:flex;gap:1rem;align-items:center;justify-content:space-between;background:var(--surface);border:1px solid var(--line);border-radius:12px;padding:.55rem 1rem;margin-bottom:1rem;box-shadow:var(--shadow);font-weight:700}
#examTimer{color:var(--accent-2);font-variant-numeric:tabular-nums;font-size:1.05rem}
#examTimer.low{color:var(--red-ink)}
.q .opt.sel{border-color:var(--accent-2);background:color-mix(in srgb,var(--accent-2) 14%,transparent);font-weight:600}
.exam-verdict{text-align:center;margin-bottom:1rem}
.exam-verdict .big{font-size:2.1rem;font-weight:800}
.pass{color:var(--green-ink)}.fail{color:var(--red-ink)}
.dom-table{width:100%;border-collapse:collapse;font-size:.88rem}
.dom-table td{padding:.45rem .5rem;border-bottom:1px solid var(--line)}
.dom-bar{height:8px;border-radius:99px;background:var(--line);overflow:hidden;min-width:80px}
.dom-bar i{display:block;height:100%;background:var(--accent-2)}

.copybtn{border:1px solid var(--line);background:var(--surface);border-radius:7px;padding:.2rem .5rem;font-size:.74rem;cursor:pointer;color:var(--accent-2);font-weight:600}
.foot{max-width:var(--maxw);margin:2rem auto;padding:1.4rem 1.2rem;border-top:1px solid var(--line);display:flex;justify-content:space-between;gap:1rem;flex-wrap:wrap;color:var(--muted);font-size:.82rem}
@media print{.topbar,.hero-cta,.tracker,#themeToggle,.skip{display:none!important}body{background:#fff}.card,.chap{box-shadow:none}}