:root{
  --bg:#0f1419; --bg2:#161c24; --card:#1c242e; --card2:#232c38;
  --border:#2c3744; --text:#e6edf3; --muted:#8b98a5; --accent:#3b82f6;
  --accent2:#2563eb; --green:#22c55e; --green-bg:#0f2e1d; --red:#ef4444;
  --red-bg:#34161a; --amber:#f59e0b; --radius:12px;
  --mono:ui-monospace,SFMono-Regular,Menlo,Consolas,monospace;
  --sans:system-ui,-apple-system,"Segoe UI",Roboto,Helvetica,Arial,sans-serif;
}
body.light{
  --bg:#eef1f6; --bg2:#ffffff; --card:#ffffff; --card2:#f1f4f9;
  --border:#d6dde7; --text:#1a2230; --muted:#5d6b7e;
  --accent:#2563eb; --accent2:#1d4ed8; --green:#15803d; --green-bg:#e6f6ec;
  --red:#dc2626; --red-bg:#fdeaea; --amber:#b45309;
}
*{box-sizing:border-box}
html,body{margin:0;padding:0}
body{background:var(--bg);color:var(--text);font-family:var(--sans);
  line-height:1.6;font-size:16px;-webkit-font-smoothing:antialiased}
.hidden{display:none !important}
em{color:var(--muted);font-style:italic}

/* buttons */
.btn{font-family:inherit;font-size:15px;font-weight:600;border:1px solid var(--border);
  background:var(--card2);color:var(--text);padding:10px 18px;border-radius:10px;
  cursor:pointer;transition:.15s;white-space:nowrap}
.btn:hover{border-color:var(--accent);background:var(--card)}
.btn:disabled{opacity:.4;cursor:not-allowed}
.btn-primary{background:var(--accent2);border-color:var(--accent2);color:#fff}
.btn-primary:hover{background:var(--accent);border-color:var(--accent)}
.btn-ghost{background:transparent}
.btn-lg{font-size:18px;padding:14px 38px;border-radius:12px}

/* theme toggle pill */
.theme-toggle{font-size:13px;padding:8px 13px;border-radius:99px;background:var(--card2);
  border:1px solid var(--border);color:var(--text);cursor:pointer;font-weight:600;
  display:inline-flex;align-items:center;gap:6px;white-space:nowrap}
.theme-toggle:hover{border-color:var(--accent)}
.theme-toggle.on-home{position:absolute;top:18px;right:18px;z-index:5}
body.light .home-card,body.light .topbar,body.light .footer{box-shadow:0 1px 3px rgba(20,30,50,.06)}

/* ---------- HOME ---------- */
.screen{min-height:100vh;display:flex;flex-direction:column}
#home{align-items:center;justify-content:center;padding:40px 24px}
.home-card{position:relative;max-width:580px;width:100%;text-align:center;background:var(--card);
  border:1px solid var(--border);border-radius:22px;padding:44px 44px 40px;
  background-image:radial-gradient(120% 80% at 50% -10%,rgba(59,130,246,.16),transparent 60%)}
.logo{width:74px;height:74px;margin:0 auto 16px;display:flex;align-items:center;justify-content:center;
  color:var(--accent);background:var(--bg2);border:1px solid var(--border);border-radius:20px}
.home-card h1{font-size:42px;margin:0 0 6px;letter-spacing:-1px}
.home-card h1 span{background:linear-gradient(90deg,var(--accent),#60a5fa);
  -webkit-background-clip:text;background-clip:text;-webkit-text-fill-color:transparent;font-weight:800}
.home-card h1 .ver{font-size:13px;font-style:normal;color:var(--muted);font-weight:600;
  border:1px solid var(--border);border-radius:99px;padding:2px 9px;vertical-align:middle;margin-left:6px}
.subtitle{color:var(--muted);margin:0 0 28px;font-size:16px}
.home-stats{display:flex;gap:16px;justify-content:center;margin-bottom:28px}
.home-stats div{background:var(--bg2);border:1px solid var(--border);border-radius:var(--radius);
  padding:16px 24px;min-width:130px}
.home-stats strong{display:block;font-size:30px;color:var(--accent)}
.home-stats span{color:var(--muted);font-size:12px;text-transform:uppercase;letter-spacing:.5px}

.btn-outline{background:transparent;border-color:var(--accent);color:var(--accent)}
.btn-outline:hover{background:var(--card2);border-color:var(--accent)}
.start-actions{display:flex;gap:12px;justify-content:center;flex-wrap:wrap;margin-bottom:18px}

.jump-row{display:flex;gap:8px;align-items:center;justify-content:center;flex-wrap:wrap;
  margin-bottom:30px;color:var(--muted);font-size:14px}
.jump-row label{font-weight:600}
.jump-row input{width:84px;font-family:inherit;font-size:15px;text-align:center;
  background:var(--bg2);color:var(--text);border:1px solid var(--border);border-radius:9px;padding:9px 10px}
.jump-row input:focus{outline:none;border-color:var(--accent)}

.instructions{text-align:left;background:var(--bg2);border:1px solid var(--border);
  border-radius:var(--radius);padding:20px 22px}
.instructions h3{margin:0 0 12px;font-size:13px;text-transform:uppercase;letter-spacing:.6px;color:var(--muted)}
.instructions ul{margin:0;padding-left:20px;font-size:14px;color:var(--text);line-height:1.7}
.instructions li{margin-bottom:6px}
.instructions strong{color:var(--text)}
.kbd-legend{display:flex;gap:18px;flex-wrap:wrap;margin-top:16px;padding-top:14px;
  border-top:1px solid var(--border);font-size:13px;color:var(--muted)}
.kbd-legend span{display:inline-flex;align-items:center;gap:6px}
kbd{font-family:var(--mono);font-size:11px;background:var(--card2);border:1px solid var(--border);
  border-bottom-width:2px;border-radius:6px;padding:2px 7px;color:var(--text)}
.home-footer{margin-top:26px;color:var(--muted);font-size:12.5px;text-align:center}

/* study by domain */
.domain-section{text-align:left;margin-bottom:24px}
.domain-section h3{margin:0 0 12px;font-size:13px;text-transform:uppercase;letter-spacing:.6px;color:var(--muted)}
.domain-section h3 em{text-transform:none;letter-spacing:0;font-size:12px}
.domain-grid{display:grid;grid-template-columns:1fr 1fr;gap:10px}
.domain-btn{display:flex;align-items:center;gap:12px;text-align:left;padding:14px 16px;
  background:var(--bg2);border:1px solid var(--border);border-radius:var(--radius);cursor:pointer;
  color:var(--text);font-family:inherit;transition:.12s}
.domain-btn:hover{border-color:var(--accent);background:var(--card2)}
.domain-btn .dnum{flex:none;width:34px;height:34px;border-radius:9px;display:flex;align-items:center;
  justify-content:center;font-weight:800;font-size:15px;color:#fff}
.domain-btn[data-domain="1"] .dnum{background:#3b82f6}
.domain-btn[data-domain="2"] .dnum{background:#8b5cf6}
.domain-btn[data-domain="3"] .dnum{background:#ef4444}
.domain-btn[data-domain="4"] .dnum{background:#10b981}
.domain-btn.pbq-only .dnum{background:var(--amber)}
.domain-btn .dinfo{display:flex;flex-direction:column;line-height:1.25}
.domain-btn .dname{font-weight:600;font-size:14px}
.domain-btn .dcount{font-size:12px;color:var(--muted)}

/* mode label in topbar */
#mode-label{color:var(--accent);font-weight:700}
#mode-label:not(:empty)::after{content:" · ";color:var(--muted);font-weight:400}

@media(max-width:520px){.domain-grid{grid-template-columns:1fr}}

/* ---------- TOPBAR ---------- */
.topbar{position:sticky;top:0;z-index:20;display:flex;align-items:center;gap:16px;
  padding:12px 20px;background:var(--bg2);border-bottom:1px solid var(--border)}
.progress-wrap{flex:1;display:flex;flex-direction:column;gap:6px}
.progress-text{font-size:13px;color:var(--muted);text-align:center;font-variant-numeric:tabular-nums}
.progress-bar{height:6px;background:var(--card2);border-radius:99px;overflow:hidden}
#progress-fill{height:100%;width:0;background:var(--accent);transition:width .3s}

/* ---------- NAVIGATOR ---------- */
.navigator{display:grid;grid-template-columns:repeat(auto-fill,minmax(46px,1fr));gap:8px;
  padding:18px 20px;background:var(--bg2);border-bottom:1px solid var(--border);
  max-height:40vh;overflow:auto}
.nav-cell{aspect-ratio:1;border:1px solid var(--border);background:var(--card);
  color:var(--muted);border-radius:8px;font-size:13px;font-weight:600;cursor:pointer;
  display:flex;align-items:center;justify-content:center;transition:.12s}
.nav-cell:hover{border-color:var(--accent);color:var(--text)}
.nav-cell.answered{background:var(--green-bg);color:var(--green);border-color:#1c5236}
.nav-cell.correct{background:var(--green-bg);color:var(--green);border-color:#1c5236}
.nav-cell.incorrect{background:var(--red-bg);color:var(--red);border-color:#5c1f25}
#score{color:var(--accent);font-weight:700}
.nav-cell.current{outline:2px solid var(--accent);outline-offset:1px;color:var(--text)}
.nav-cell.pbq{font-style:italic}

/* ---------- QUESTION ---------- */
.question-area{flex:1;width:100%;max-width:860px;margin:0 auto;padding:32px 24px 60px}
.q-meta{display:flex;align-items:center;gap:10px;margin-bottom:14px}
.q-number{font-size:14px;font-weight:700;color:var(--accent);text-transform:uppercase;letter-spacing:.6px}
.tag{font-size:11px;font-weight:700;text-transform:uppercase;letter-spacing:.5px;
  padding:3px 9px;border-radius:99px;border:1px solid}
.tag-pbq{color:var(--amber);border-color:#7c5a12;background:#2a2110}
.q-stem{font-size:18px;margin:0 0 22px}
.q-stem p{margin:0 0 12px}
.q-images{display:flex;flex-direction:column;gap:14px;margin:0 0 24px}
.q-images img{max-width:100%;border:1px solid var(--border);border-radius:10px;
  background:#fff;cursor:zoom-in;display:block}

/* options */
.options{display:flex;flex-direction:column;gap:10px;margin-bottom:8px}
.option{display:flex;gap:14px;align-items:flex-start;padding:14px 16px;border:1px solid var(--border);
  background:var(--card);border-radius:var(--radius);cursor:pointer;transition:.12s}
.option:hover{border-color:var(--accent)}
.option.selected{border-color:var(--accent);background:var(--card2)}
.option .letter{flex:none;width:28px;height:28px;border-radius:7px;background:var(--bg2);
  border:1px solid var(--border);display:flex;align-items:center;justify-content:center;
  font-weight:700;font-size:14px}
.option .otext{flex:1;padding-top:2px}
.option.correct{border-color:var(--green);background:var(--green-bg)}
.option.correct .letter{background:var(--green);color:#04140b;border-color:var(--green)}
.option.incorrect{border-color:var(--red);background:var(--red-bg)}
.option.incorrect .letter{background:var(--red);color:#fff;border-color:var(--red)}
.options.locked .option{cursor:default}

/* explanation panel */
.explain{margin-top:26px;border:1px solid var(--border);border-radius:var(--radius);overflow:hidden}
.explain-head{padding:14px 18px;font-weight:700;background:var(--green-bg);color:var(--green);
  border-bottom:1px solid var(--border)}
.explain-body{padding:18px}
.explain h4{margin:22px 0 8px;font-size:13px;text-transform:uppercase;letter-spacing:.6px;color:var(--muted)}
.explain h4:first-child{margin-top:0}
.explain p{margin:0 0 12px}
.block{background:var(--bg2);border:1px solid var(--border);border-radius:10px;padding:14px 16px;
  white-space:pre-wrap;font-size:14.5px}
.block.refs{font-family:var(--mono);font-size:13px;color:var(--muted);line-height:1.7}
.block a{color:var(--accent);word-break:break-all}
.answer-pill{display:inline-block;background:var(--green);color:#04140b;font-weight:800;
  padding:4px 14px;border-radius:99px;font-size:15px}
/* interactive PBQ form */
.pbq-form{display:flex;flex-direction:column;gap:16px;margin:4px 0 8px;
  background:var(--bg2);border:1px solid var(--border);border-radius:var(--radius);padding:18px 20px}
.pbq-instr{margin:0 0 4px;color:var(--muted);font-size:14px}
.pbq-part{display:flex;flex-direction:column;gap:7px}
.pbq-label{font-weight:600;font-size:15px}
.pbq-select,.pbq-input{font-family:inherit;font-size:15px;padding:10px 12px;border-radius:9px;
  background:var(--card);color:var(--text);border:1px solid var(--border);max-width:420px}
.pbq-input{width:160px}
.pbq-select:focus,.pbq-input:focus{outline:none;border-color:var(--accent)}
.pbq-result{display:flex;flex-wrap:wrap;gap:6px 16px;align-items:center;font-weight:600;
  padding:10px 14px;border-radius:9px;border:1px solid;max-width:420px}
.pbq-result.correct{background:var(--green-bg);color:var(--green);border-color:#1c5236}
.pbq-result.incorrect{background:var(--red-bg);color:var(--red);border-color:#5c1f25}
.pbq-result.neutral{background:var(--bg2);color:var(--muted);border-color:var(--border)}
.pbq-corr{color:var(--green);font-weight:700}
.reco-grid{display:flex;flex-direction:column;gap:8px}
.reco-row{display:flex;gap:8px;align-items:center}
.reco-row>select,.reco-row>span{flex:1;min-width:0}
.reco-row .pbq-select{max-width:none;width:100%}
.reco-head{font-size:11px;text-transform:uppercase;letter-spacing:.5px;color:var(--muted);font-weight:700}
.reco-row.row-correct{color:var(--green)}
.reco-row.row-incorrect{color:var(--red)}
.reco-mark{flex:0 0 22px;text-align:center;font-weight:800}
.reco-key{margin-top:12px;font-size:14px;color:var(--muted)}
.reco-key ul{margin:6px 0 0;padding-left:20px;color:var(--text)}
.reco-key li{margin-bottom:3px}
.pbq-checkset{display:flex;flex-direction:column;gap:7px}
.pbq-check{display:flex;align-items:flex-start;gap:8px;font-size:14px;cursor:pointer}
.pbq-check input{margin-top:3px}
.pbq-check.fp-correct{color:var(--green);font-weight:600}
.pbq-check.fp-wrong{color:var(--red);font-weight:600}
.fp-tag{font-weight:700}
.pbq-multi{display:flex;flex-direction:column;gap:6px}
.pbq-multi .pbq-select{max-width:none;width:100%}

.note-box{background:#3a2f10;border:1px solid var(--amber);border-left-width:4px;
  border-radius:8px;padding:12px 16px;margin-bottom:18px;font-size:14.5px;color:#fde9c4}
.note-box strong{color:var(--amber)}
body.light .note-box{background:#fef6e3;color:#5a4408}

/* footer */
.footer{position:sticky;bottom:0;display:flex;gap:12px;align-items:center;justify-content:space-between;
  padding:14px 20px;background:var(--bg2);border-top:1px solid var(--border)}
.footer #check-btn{flex:1;max-width:260px;margin:0 auto}

/* lightbox */
.lightbox{position:fixed;inset:0;background:rgba(0,0,0,.88);display:flex;align-items:center;
  justify-content:center;z-index:100;cursor:zoom-out;padding:24px}
.lightbox img{max-width:100%;max-height:100%;border-radius:8px}

@media(max-width:640px){
  .home-card{padding:34px 22px}
  .home-card h1{font-size:34px}
  .question-area{padding:22px 16px 50px}
  .q-stem{font-size:16.5px}
  .footer .btn{padding:10px 12px}
}