:root{
  --brand:#0b4f8a; --brand-d:#083a66; --brand-l:#e8f1fa;
  --accent:#38bdf8; --accent-d:#0ea5e9;
  --ink:#0a1f33; --muted:#5b6b7c; --line:#dde6ef;
  --bg:#f5f8fb; --card:#ffffff;
  --ok:#15803d; --ok-l:#e8f7ee; --bad:#c62828; --bad-l:#fdecec; --warn:#b45309; --warn-l:#fff4e0;
  --radius:16px; --shadow:0 4px 18px rgba(10,31,51,.07);
}
*{box-sizing:border-box}
body{margin:0;font-family:"Be Vietnam Pro",system-ui,-apple-system,"Segoe UI",Roboto,sans-serif;color:var(--ink);background:var(--bg);line-height:1.55;font-size:16px;min-height:100vh;display:flex;flex-direction:column}
img{max-width:100%;display:block}
a{color:var(--brand)}
button{font:inherit;color:inherit}
.wrap{max-width:860px;margin:0 auto;padding:0 16px;width:100%}
main{flex:1;padding:20px 16px 40px;outline:none}
h1,h2,h3{line-height:1.25;margin:0 0 10px}
h1{font-size:clamp(1.35rem,4vw,1.8rem);font-weight:800}
h2{font-size:1.15rem;font-weight:800}
.muted{color:var(--muted)}
.small{font-size:.86rem}

/* Header */
.top{position:sticky;top:0;z-index:40;background:rgba(255,255,255,.96);backdrop-filter:blur(8px);border-bottom:1px solid var(--line)}
.nav{display:flex;align-items:center;justify-content:space-between;height:60px;gap:12px}
.logo{display:flex;align-items:center;gap:8px;text-decoration:none;color:var(--ink);min-width:0}
.logo img{width:40px;height:40px;object-fit:contain;flex:none}
.logo b{display:block;font-weight:900;font-size:1.05rem;line-height:1;color:var(--brand)}
.logo b span{color:var(--accent)}
.logo small{display:block;font-size:.72rem;font-weight:700;color:var(--muted);margin-top:3px}
.lic-pick{display:flex;align-items:center;gap:8px;font-weight:700;font-size:.9rem}
.lic-pick select{font:inherit;font-weight:700;padding:8px 10px;border:1.5px solid var(--line);border-radius:10px;background:#fff;color:var(--brand)}

/* Generic */
.card{background:var(--card);border:1px solid var(--line);border-radius:var(--radius);padding:18px;box-shadow:var(--shadow)}
.btn{display:inline-flex;align-items:center;justify-content:center;gap:8px;padding:12px 18px;border-radius:12px;font-weight:700;text-decoration:none;border:1.5px solid transparent;cursor:pointer;font-size:.97rem;background:var(--brand);color:#fff;transition:background .15s,transform .1s}
.btn:active{transform:scale(.98)}
.btn:hover{background:var(--brand-d)}
.btn.ghost{background:#fff;color:var(--brand);border-color:var(--line)}
.btn.ghost:hover{background:var(--brand-l)}
.btn.danger{background:var(--bad)}
.btn.danger:hover{background:#a51f1f}
.btn.accent{background:var(--accent);color:var(--ink)}
.btn.accent:hover{background:var(--accent-d)}
.btn:disabled{opacity:.45;cursor:default}
.btn.sm{padding:8px 12px;font-size:.88rem;border-radius:10px}
.back{display:inline-flex;align-items:center;gap:6px;text-decoration:none;font-weight:700;font-size:.92rem;margin-bottom:12px}
.state{text-align:center;padding:64px 16px;color:var(--muted)}
.spinner{width:36px;height:36px;border-radius:50%;border:4px solid var(--brand-l);border-top-color:var(--brand);margin:0 auto 14px;animation:spin .8s linear infinite}
@keyframes spin{to{transform:rotate(360deg)}}
.badge{display:inline-flex;align-items:center;gap:4px;font-size:.75rem;font-weight:800;padding:3px 9px;border-radius:999px;background:var(--bad-l);color:var(--bad);white-space:nowrap}
.bar{height:8px;border-radius:99px;background:var(--brand-l);overflow:hidden}
.bar i{display:block;height:100%;background:var(--brand);border-radius:99px}

/* Home */
.hello{background:linear-gradient(135deg,var(--brand-d),var(--brand) 65%,#1673c4);color:#fff;border-radius:20px;padding:22px;margin-bottom:18px}
.hello p{margin:0;opacity:.9}
.rules{display:flex;flex-wrap:wrap;gap:8px;margin-top:14px}
.rules span{background:rgba(255,255,255,.14);border:1px solid rgba(255,255,255,.25);padding:5px 12px;border-radius:999px;font-size:.85rem;font-weight:600}
.menu{display:grid;gap:12px;grid-template-columns:1fr 1fr}
@media(min-width:720px){.menu{grid-template-columns:repeat(4,1fr)}}
.tile{display:flex;flex-direction:column;gap:6px;text-decoration:none;color:var(--ink);background:#fff;border:1px solid var(--line);border-radius:var(--radius);padding:16px;box-shadow:var(--shadow);transition:transform .15s,border-color .15s}
.tile:hover{transform:translateY(-2px);border-color:var(--brand)}
.tile .ico{font-size:1.6rem}
.tile b{font-size:1rem}
.tile span{font-size:.84rem;color:var(--muted)}
.tile.main{grid-column:span 2;background:var(--brand-l);border-color:#c9dcf0}
@media(min-width:720px){.tile.main{grid-column:span 2}}
.section-title{margin:26px 0 10px;font-size:1.05rem}
.promo{display:flex;flex-wrap:wrap;gap:12px;align-items:center;justify-content:space-between;margin-top:24px;background:#fff;border:1px dashed var(--brand);border-radius:var(--radius);padding:16px}
.promo p{margin:0;font-weight:600}

/* Topic list */
.topics{display:grid;gap:10px}
.topic{display:flex;gap:14px;align-items:center;text-decoration:none;color:var(--ink);background:#fff;border:1px solid var(--line);border-radius:14px;padding:14px 16px;transition:border-color .15s}
.topic:hover{border-color:var(--brand)}
.topic .ico{width:42px;height:42px;border-radius:12px;background:var(--brand-l);display:grid;place-items:center;font-size:1.2rem;flex:none}
.topic.crit .ico{background:var(--bad-l)}
.topic .body{flex:1;min-width:0}
.topic b{display:block;font-size:.98rem}
.topic .meta{display:flex;justify-content:space-between;gap:8px;font-size:.8rem;color:var(--muted);margin-top:6px}
.topic .bar{margin-top:6px}
.toolbar{display:flex;flex-wrap:wrap;gap:10px;align-items:center;justify-content:space-between;margin-bottom:14px}

/* Question */
.qhead{display:flex;flex-wrap:wrap;align-items:center;justify-content:space-between;gap:10px;margin-bottom:12px}
.qhead h1{font-size:1.1rem;margin:0}
.timer{font-variant-numeric:tabular-nums;font-weight:800;font-size:1.25rem;padding:6px 14px;border-radius:12px;background:var(--brand-l);color:var(--brand)}
.timer.warn{background:var(--bad-l);color:var(--bad);animation:blink 1s steps(2) infinite}
@keyframes blink{50%{opacity:.6}}
.qcard{background:#fff;border:1px solid var(--line);border-radius:var(--radius);padding:18px;box-shadow:var(--shadow)}
.qtop{display:flex;justify-content:space-between;align-items:flex-start;gap:12px;margin-bottom:8px}
.qno{font-weight:800;color:var(--brand);font-size:.9rem}
.qtext{font-weight:700;font-size:1.06rem;white-space:pre-line;margin:4px 0 14px}
.mark{border:1.5px solid var(--line);background:#fff;border-radius:10px;padding:6px 10px;cursor:pointer;font-size:.85rem;font-weight:700;color:var(--muted);flex:none}
.mark[aria-pressed=true]{color:var(--warn);border-color:#f3c98b;background:var(--warn-l)}
.qimg{margin:0 0 14px;border-radius:12px;overflow:hidden;border:1px solid var(--line);background:#fafcfe;cursor:zoom-in;display:block;padding:0;width:100%}
.qimg img{margin:0 auto;max-height:340px;width:auto;object-fit:contain}
.opts{display:grid;gap:10px}
.opt{display:flex;gap:12px;align-items:flex-start;text-align:left;width:100%;padding:13px 14px;border:1.5px solid var(--line);border-radius:12px;background:#fff;cursor:pointer;font-size:.98rem;line-height:1.45;transition:border-color .12s,background .12s}
.opt:hover:not(:disabled){border-color:var(--brand)}
.opt:disabled{cursor:default}
.opt .n{width:28px;height:28px;flex:none;border-radius:8px;background:var(--brand-l);color:var(--brand);font-weight:800;display:grid;place-items:center;font-size:.9rem}
.opt.sel{border-color:var(--brand);background:var(--brand-l)}
.opt.sel .n{background:var(--brand);color:#fff}
.opt.ok{border-color:var(--ok);background:var(--ok-l)}
.opt.ok .n{background:var(--ok);color:#fff}
.opt.bad{border-color:var(--bad);background:var(--bad-l)}
.opt.bad .n{background:var(--bad);color:#fff}
.verdict{margin-top:14px;padding:12px 14px;border-radius:12px;font-weight:700}
.verdict.ok{background:var(--ok-l);color:var(--ok)}
.verdict.bad{background:var(--bad-l);color:var(--bad)}
.qnav{display:flex;gap:10px;align-items:center;justify-content:space-between;margin-top:14px}
.qnav .btn{flex:1}
.qnav .mid{flex:0 0 auto}

/* Grid */
.grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(44px,1fr));gap:6px;margin-top:14px}
.cell{position:relative;height:40px;border-radius:9px;border:1.5px solid var(--line);background:#fff;font-weight:700;font-size:.85rem;cursor:pointer;font-variant-numeric:tabular-nums}
.cell.done{background:var(--brand-l);border-color:#c9dcf0;color:var(--brand)}
.cell.ok{background:var(--ok-l);border-color:#9fd7b3;color:var(--ok)}
.cell.bad{background:var(--bad-l);border-color:#f2b0b0;color:var(--bad)}
.cell.cur{outline:3px solid var(--accent);outline-offset:1px}
.cell.crit::after{content:"";position:absolute;top:3px;right:3px;width:7px;height:7px;border-radius:50%;background:var(--bad)}
.legend{display:flex;flex-wrap:wrap;gap:12px;font-size:.78rem;color:var(--muted);margin-top:10px}
.legend i{display:inline-block;width:12px;height:12px;border-radius:3px;vertical-align:-1px;margin-right:4px;border:1.5px solid var(--line)}
details.gridbox{margin-top:14px}
details.gridbox summary{cursor:pointer;font-weight:700;color:var(--brand);font-size:.92rem}

/* Exam list */
.exams{display:grid;gap:10px;grid-template-columns:repeat(3,1fr)}
@media(min-width:640px){.exams{grid-template-columns:repeat(5,1fr)}}
.exam{position:relative;display:flex;flex-direction:column;align-items:center;justify-content:center;gap:2px;min-height:84px;text-decoration:none;color:var(--ink);background:#fff;border:1.5px solid var(--line);border-radius:14px;padding:10px 6px;cursor:pointer;text-align:center}
.exam:hover{border-color:var(--brand)}
.exam b{font-size:.98rem}
.exam span{font-size:.78rem;color:var(--muted)}
.exam.pass{background:var(--ok-l);border-color:#9fd7b3}
.exam.pass span.sc{color:var(--ok);font-weight:800}
.exam.fail{background:var(--bad-l);border-color:#f2b0b0}
.exam.fail span.sc{color:var(--bad);font-weight:800}
.exam.draft{border-style:dashed;border-color:var(--warn)}
.exam.rand{background:var(--brand);color:#fff;border-color:var(--brand)}
.exam.rand span{color:rgba(255,255,255,.85)}

/* Result */
.result{text-align:center;padding:22px}
.result .big{font-size:2rem;font-weight:900;margin:6px 0}
.result.pass .big{color:var(--ok)}
.result.fail .big{color:var(--bad)}
.stats{display:grid;grid-template-columns:repeat(3,1fr);gap:10px;margin-top:16px}
.stat{border-radius:12px;padding:10px;background:var(--bg)}
.stat b{display:block;font-size:1.3rem}
.stat.ok b{color:var(--ok)} .stat.bad b{color:var(--bad)}
.reasons{list-style:none;padding:0;margin:12px 0 0;color:var(--bad);font-weight:600;font-size:.92rem}
.actions{display:flex;flex-wrap:wrap;gap:10px;justify-content:center;margin-top:18px}

/* History */
.hist{display:grid;gap:10px}
.hrow{display:flex;gap:12px;align-items:center;justify-content:space-between;text-decoration:none;color:var(--ink);background:#fff;border:1px solid var(--line);border-radius:14px;padding:12px 16px}
.hrow:hover{border-color:var(--brand)}
.pill{font-weight:800;font-size:.8rem;padding:4px 10px;border-radius:999px;white-space:nowrap}
.pill.pass{background:var(--ok-l);color:var(--ok)}
.pill.fail{background:var(--bad-l);color:var(--bad)}
.pill.draft{background:var(--warn-l);color:var(--warn)}
.empty{text-align:center;padding:40px 16px;color:var(--muted)}
.empty .ico{font-size:2.4rem}

/* Dialog */
.dlg{border:0;border-radius:18px;padding:0;max-width:420px;width:calc(100% - 32px);box-shadow:0 20px 60px rgba(0,0,0,.25)}
.dlg::backdrop,.img-dlg::backdrop{background:rgba(6,17,29,.55)}
.dlg form{padding:22px}
.dlg p{color:var(--muted);margin:0 0 18px}
.dlg-actions{display:flex;gap:10px;justify-content:flex-end;flex-wrap:wrap}
.img-dlg{border:0;padding:0;background:transparent;max-width:min(96vw,900px);max-height:92vh}
.img-dlg img{max-height:88vh;border-radius:12px;background:#fff}
.img-close{position:absolute;top:8px;right:8px;width:36px;height:36px;border-radius:50%;border:0;background:rgba(0,0,0,.6);color:#fff;cursor:pointer;font-size:1rem}

.foot{background:#06111d;color:rgba(255,255,255,.7);font-size:.85rem;padding:22px 0}
.foot p{margin:4px 0}
.foot a{color:#fff;text-decoration:none}
kbd{font:inherit;font-size:.75rem;border:1px solid var(--line);border-bottom-width:2px;border-radius:5px;padding:0 5px;background:#fff}
.hint{font-size:.78rem;color:var(--muted);margin-top:10px;text-align:center}
@media(max-width:640px){.hint{display:none}}
@media (prefers-reduced-motion:reduce){*{animation:none!important;transition:none!important}}

/* Tìm câu hỏi */
.search{display:flex;gap:8px;margin:0 0 16px}
.search input{flex:1;min-width:0;font:inherit;padding:12px 14px;border:1.5px solid var(--line);border-radius:12px;background:#fff;color:var(--ink)}
.search input:focus{outline:3px solid var(--accent);outline-offset:1px;border-color:var(--brand)}
.hits{display:grid;gap:10px}
.hit{background:#fff;border:1px solid var(--line);border-radius:14px;padding:12px 16px}
.hit[open]{border-color:var(--brand)}
.hit summary{cursor:pointer;list-style:none;display:flex;flex-direction:column;gap:4px}
.hit summary::-webkit-details-marker{display:none}
.hit .htext{font-weight:600}
.hit .qimg{margin-top:12px}
.hit-opts{margin:12px 0;padding-left:22px}
.hit-opts li{padding:4px 6px;border-radius:8px;margin-bottom:4px}
.hit-opts li.ok{background:var(--ok-l);color:var(--ok);font-weight:700}
mark{background:#fff1a8;color:inherit;border-radius:3px;padding:0 1px}

/* Mẹo ghi nhớ cạnh chủ đề */
.topic-row{display:flex;gap:8px}
.topic-row .topic{flex:1;min-width:0}
.tip-link{flex:none;display:flex;flex-direction:column;align-items:center;justify-content:center;gap:2px;width:64px;text-decoration:none;background:var(--warn-l);border:1px solid #f3c98b;border-radius:14px;font-size:1.2rem}
.tip-link span{font-size:.75rem;font-weight:700;color:var(--warn)}
.tip-link:hover{border-color:var(--warn)}
a.promo{text-decoration:none;color:var(--ink)}
.tip-promo{border-color:#f3c98b;background:var(--warn-l)}