/* ===================== F&D Arena ===================== */
:root{
  --bg:#F4F6FB; --paper:#FFFFFF; --paper-2:#EEF1F8; --ink:#101733; --ink-2:#434D6B; --ink-3:#687190; --line:#E1E5EF;
  --navy:#1D2B5C; --deep:#101B45; --sun:#FFC233; --sun-soft:rgba(255,194,51,.2); --link:#2B48C8; --btn:#1D2B5C; --btn-ink:#fff; --focus:#2B48C8;
  --good:#0F8A5F; --good-soft:rgba(15,138,95,.12); --bad:#C8363D; --bad-soft:rgba(200,54,61,.10); --warn:#A86A00; --warn-soft:rgba(255,194,51,.22);
  --e:#0F8A5F; --m:#A86A00; --h:#C8363D;
  --shadow:0 1px 2px rgba(16,23,51,.04),0 10px 30px -12px rgba(16,23,51,.18);
  --f:"Be Vietnam Pro",system-ui,-apple-system,"Segoe UI",sans-serif; --mono:"JetBrains Mono",ui-monospace,Menlo,monospace;
}
@media (prefers-color-scheme: dark){
  :root:not([data-theme="light"]){
    color-scheme:dark; --bg:#0A0F22; --paper:#111934; --paper-2:#19223F; --ink:#EDF0FA; --ink-2:#B3BAD2; --ink-3:#8A92B0; --line:#252E52;
    --link:#A3B3FF; --btn:#FFC233; --btn-ink:#1A1300; --focus:#A3B3FF; --good:#45C994; --good-soft:rgba(69,201,148,.14); --bad:#FF7C80; --bad-soft:rgba(255,124,128,.12);
    --warn:#FFC24D; --warn-soft:rgba(255,194,51,.16); --e:#45C994; --m:#FFC24D; --h:#FF7C80; --shadow:0 1px 2px rgba(0,0,0,.4),0 10px 30px -12px rgba(0,0,0,.6);
  }
}
:root[data-theme="dark"]{
  color-scheme:dark; --bg:#0A0F22; --paper:#111934; --paper-2:#19223F; --ink:#EDF0FA; --ink-2:#B3BAD2; --ink-3:#8A92B0; --line:#252E52;
  --link:#A3B3FF; --btn:#FFC233; --btn-ink:#1A1300; --focus:#A3B3FF; --good:#45C994; --good-soft:rgba(69,201,148,.14); --bad:#FF7C80; --bad-soft:rgba(255,124,128,.12);
  --warn:#FFC24D; --warn-soft:rgba(255,194,51,.16); --e:#45C994; --m:#FFC24D; --h:#FF7C80; --shadow:0 1px 2px rgba(0,0,0,.4),0 10px 30px -12px rgba(0,0,0,.6);
}
:root[data-theme="light"]{color-scheme:light}
*{box-sizing:border-box}
html,body{margin:0}
body{background:var(--bg);color:var(--ink);font:15px/1.55 var(--f);-webkit-font-smoothing:antialiased;overflow-x:clip}
a{color:var(--link)}
button,input,select,textarea{font:inherit;color:inherit}
:focus-visible{outline:2px solid var(--focus);outline-offset:2px}
.wrap{max-width:1180px;margin:0 auto;padding-inline:16px}
.pad{padding:24px 0}
.hint{color:var(--ink-3);font-size:13.5px}
.muted{color:var(--ink-2)}
[hidden]{display:none !important}

/* nav */
.nav{position:sticky;top:0;z-index:20;background:color-mix(in srgb,var(--paper) 88%,transparent);backdrop-filter:blur(12px);border-bottom:1px solid var(--line)}
.nav .wrap{display:flex;align-items:center;gap:18px;min-height:60px}
.brand{display:flex;align-items:center;gap:10px;text-decoration:none;color:var(--ink);font-weight:900;font-size:19px;white-space:nowrap}
.brand b{color:var(--sun)} .brand em{font-style:normal;color:var(--ink-2);font-weight:700}
.links{display:flex;gap:4px;flex:1;overflow-x:auto}
.links a{padding:8px 12px;border-radius:9px;text-decoration:none;color:var(--ink-2);font-weight:600;white-space:nowrap}
.links a.on{background:var(--paper-2);color:var(--ink)}
.right{display:flex;align-items:center;gap:8px}
.me{display:flex;align-items:center;gap:8px;font-weight:600;font-size:14px}
.foot{display:flex;justify-content:space-between;gap:12px;flex-wrap:wrap;padding-block:30px;color:var(--ink-3);font-size:13px}
.foot a{color:var(--ink-3);margin-left:12px}
@media (max-width:720px){.nav .wrap{flex-wrap:wrap;gap:6px 10px;padding-block:8px}.links{order:3;flex-basis:100%}.brand{font-size:17px}}

/* buttons, inputs, cards */
.btn{border:1px solid var(--line);background:var(--paper);border-radius:10px;padding:8px 14px;font-size:14px;font-weight:600;display:inline-flex;align-items:center;justify-content:center;gap:6px;text-decoration:none;color:var(--ink);cursor:pointer;white-space:nowrap}
.btn:hover{border-color:var(--ink-3)}
.btn:disabled{opacity:.5;cursor:not-allowed}
.btn.primary{background:var(--btn);border-color:var(--btn);color:var(--btn-ink)}
.btn.sun{background:var(--sun);border-color:var(--sun);color:#1A1300}
.btn.ghost{background:transparent;border-color:transparent}
.btn.danger{color:var(--bad)}
.btn.good{color:var(--good)}
.btn.sm{padding:5px 10px;font-size:13px;border-radius:8px}
.btn.lg{padding:12px 22px;font-size:16px;border-radius:12px}
.btn.sq{width:36px;height:36px;padding:0}
.card{background:var(--paper);border:1px solid var(--line);border-radius:16px;box-shadow:var(--shadow)}
label.f{display:grid;gap:5px;font-weight:600;font-size:13.5px}
input[type=text],input[type=email],input[type=password],input[type=number],input[type=search],input[type=datetime-local],select,textarea{width:100%;border:1px solid var(--line);background:var(--paper);border-radius:10px;padding:9px 11px;font-size:14.5px}
textarea{min-height:90px;resize:vertical;line-height:1.5}
.err{color:var(--bad);background:var(--bad-soft);border-radius:10px;padding:10px 12px;font-size:14px}
.ok{color:var(--good);background:var(--good-soft);border-radius:10px;padding:10px 12px;font-size:14px}
.warnbox{background:var(--warn-soft);border-radius:10px;padding:10px 12px;font-size:14px}
.section-head{display:flex;justify-content:space-between;align-items:flex-end;gap:16px;flex-wrap:wrap;margin:26px 0 18px}
.section-head h1{margin:0;font-size:30px;line-height:1.15;letter-spacing:-.3px}
.section-head p{margin:6px 0 0;color:var(--ink-2)}
.eyebrow{font-size:12px;font-weight:800;letter-spacing:1px;text-transform:uppercase;color:var(--warn)}
.toast{position:fixed;left:50%;bottom:22px;transform:translateX(-50%);z-index:60;background:var(--ink);color:var(--bg);padding:11px 16px;border-radius:12px;font-weight:600;max-width:min(560px,calc(100% - 32px));box-shadow:var(--shadow)}
.scrim{position:fixed;inset:0;background:rgba(8,10,24,.5);z-index:40}
.modal{position:fixed;z-index:41;left:50%;top:50%;transform:translate(-50%,-50%);width:min(820px,calc(100% - 24px));max-height:calc(100% - 24px);overflow:auto;padding:20px;display:grid;gap:14px}
.modal.sm{width:min(480px,calc(100% - 24px))}
.modal h2{margin:0;font-size:20px}
.row{display:flex;gap:10px;flex-wrap:wrap;align-items:center}
.grid2{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:12px}
.grid3{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:12px}
.grid4{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));gap:12px}
@media (max-width:720px){.grid3,.grid4{grid-template-columns:repeat(2,minmax(0,1fr))}.grid2{grid-template-columns:1fr}}
.pill{display:inline-flex;align-items:center;gap:4px;padding:2px 9px;border-radius:99px;font-size:12px;font-weight:700;background:var(--paper-2);color:var(--ink-2);white-space:nowrap}
.pill.easy{color:var(--e);background:color-mix(in srgb,var(--e) 14%,transparent)}
.pill.medium{color:var(--m);background:color-mix(in srgb,var(--m) 16%,transparent)}
.pill.hard{color:var(--h);background:color-mix(in srgb,var(--h) 14%,transparent)}
.pill.approved,.pill.published{color:var(--good);background:var(--good-soft)}
.pill.review{color:var(--link);background:color-mix(in srgb,var(--link) 14%,transparent)}
.pill.draft{color:var(--ink-3)}
.pill.archived,.pill.closed{color:var(--ink-3);text-decoration:line-through}
.code{font-family:var(--mono);font-size:12.5px;font-weight:700;color:var(--ink-2)}

/* đăng nhập */
.auth{max-width:420px;margin:40px auto;padding:26px;display:grid;gap:14px}
.auth h1{margin:0;font-size:26px}

/* danh sách bài thi */
.exams{display:grid;grid-template-columns:repeat(auto-fill,minmax(290px,1fr));gap:16px}
.exam-card{padding:18px;display:grid;gap:10px;align-content:start;text-decoration:none;color:inherit}
.exam-card h3{margin:0;font-size:18px;line-height:1.3}
.exam-card .meta{display:flex;flex-wrap:wrap;gap:6px}
.state{font-size:12px;font-weight:800;letter-spacing:.5px}
.state.open{color:var(--good)} .state.soon{color:var(--warn)} .state.closed{color:var(--ink-3)}
.empty{padding:40px;text-align:center;color:var(--ink-2)}

/* làm bài */
.play{display:grid;grid-template-columns:minmax(0,1fr) 260px;gap:18px;margin-top:18px;align-items:start}
@media (max-width:860px){.play{grid-template-columns:1fr}}
.qcard{padding:22px;display:grid;gap:16px}
.qhead{display:flex;justify-content:space-between;gap:10px;align-items:center;flex-wrap:wrap}
.qtext{font-size:18px;line-height:1.6;font-weight:600;overflow-wrap:anywhere}
.qimg{max-width:100%;max-height:360px;border-radius:12px;border:1px solid var(--line);background:#fff}
.opts{display:grid;gap:10px}
.opt{display:flex;gap:12px;align-items:flex-start;padding:13px 14px;border:2px solid var(--line);border-radius:12px;background:var(--paper);cursor:pointer;text-align:left;width:100%;font-size:15.5px;line-height:1.5}
.opt:hover{border-color:var(--ink-3)}
.opt .lb{flex:none;width:30px;height:30px;border-radius:50%;display:grid;place-items:center;font-weight:800;background:var(--paper-2)}
.opt.sel{border-color:var(--btn);background:color-mix(in srgb,var(--btn) 8%,var(--paper))}
.opt.sel .lb{background:var(--btn);color:var(--btn-ink)}
.opt.right{border-color:var(--good);background:var(--good-soft)}
.opt.wrong{border-color:var(--bad);background:var(--bad-soft)}
.numin{max-width:260px;font-size:18px !important;font-weight:700}
.side{position:sticky;top:76px;padding:16px;display:grid;gap:14px}
.timer{font-family:var(--mono);font-size:30px;font-weight:700;text-align:center;letter-spacing:1px}
.timer.low{color:var(--bad)}
.qnav{display:grid;grid-template-columns:repeat(5,1fr);gap:6px}
.qnav button{height:36px;border-radius:9px;border:1px solid var(--line);background:var(--paper);font-weight:700;cursor:pointer}
.qnav button.done{background:var(--btn);color:var(--btn-ink);border-color:var(--btn)}
.qnav button.cur{outline:2px solid var(--sun);outline-offset:1px}
.savestate{font-size:12.5px;color:var(--ink-3);text-align:center}
.navbtns{display:flex;justify-content:space-between;gap:10px}

/* kết quả */
.score{display:flex;align-items:center;gap:22px;padding:22px;flex-wrap:wrap}
.score .big{font-size:46px;font-weight:900;line-height:1}
.score .big small{font-size:20px;color:var(--ink-3)}
.review{display:grid;gap:14px;margin-top:16px}
.review .qcard{border-left:5px solid var(--line)}
.review .qcard.ok{border-left-color:var(--good)} .review .qcard.no{border-left-color:var(--bad)}
.explain{background:var(--paper-2);border-radius:12px;padding:12px 14px;font-size:14.5px}
.lb-table{width:100%;border-collapse:collapse}
.lb-table td,.lb-table th{padding:8px 10px;border-bottom:1px solid var(--line);text-align:left;font-size:14px}
.lb-table tr.me td{background:var(--sun-soft);font-weight:700}

/* quản trị */
.toolbar{display:flex;flex-wrap:wrap;gap:8px;align-items:center;margin-bottom:12px}
.filters{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));gap:8px;padding:14px;margin-bottom:12px}
@media (max-width:900px){.filters{grid-template-columns:repeat(2,minmax(0,1fr))}}
.filters .wide{grid-column:span 2}
.tablewrap{overflow-x:auto;border:1px solid var(--line);border-radius:14px;background:var(--paper)}
table.t{width:100%;border-collapse:collapse;font-size:13.5px}
table.t th{position:sticky;top:0;background:var(--paper-2);text-align:left;font-size:12px;text-transform:uppercase;letter-spacing:.4px;color:var(--ink-2);padding:9px 10px;white-space:nowrap}
table.t td{padding:8px 10px;border-top:1px solid var(--line);vertical-align:top}
table.t tr:hover td{background:color-mix(in srgb,var(--paper-2) 60%,transparent)}
table.t td.txt{max-width:340px;overflow:hidden;text-overflow:ellipsis;white-space:nowrap}
table.t tr.bad td{background:var(--bad-soft)}
table.t tr.warn td{background:var(--warn-soft)}
.acts{display:flex;gap:4px;flex-wrap:nowrap}
.selbar{position:sticky;bottom:12px;z-index:5;display:flex;gap:8px;align-items:center;flex-wrap:wrap;padding:10px 14px;margin-top:12px}
.optrow{display:grid;grid-template-columns:34px minmax(0,1fr) auto auto;gap:8px;align-items:center}
.optrow .lb{width:30px;height:30px;border-radius:50%;display:grid;place-items:center;font-weight:800;background:var(--paper-2)}
.check{display:inline-flex;gap:6px;align-items:center;font-weight:600;font-size:13.5px;cursor:pointer;white-space:nowrap}
.preview{border:2px dashed var(--line);border-radius:14px;padding:14px}
.preview .opt{cursor:default}
.tabs{display:flex;gap:4px;padding:4px;background:var(--paper-2);border-radius:12px;width:max-content;max-width:100%;overflow-x:auto;margin-bottom:14px}
.tabs button{border:0;background:transparent;padding:7px 13px;border-radius:9px;font-weight:600;color:var(--ink-2);cursor:pointer;white-space:nowrap}
.tabs button.on{background:var(--paper);color:var(--ink);box-shadow:var(--shadow)}
.drop{border:2px dashed var(--line);border-radius:14px;padding:26px;text-align:center;display:grid;gap:10px;justify-items:center}
.katex{font-size:1.05em}