:root{
  --bg:#f4f6fb;
  --panel:#ffffff;
  --ink:#0f172a;
  --muted:#64748b;
  --line:#e6e9f2;
  --brand:#2563eb;
  --brand-700:#1d4ed8;
  --brand-50:#eff4ff;
  --green:#16a34a;
  --green-50:#ecfdf3;
  --red:#dc2626;
  --red-50:#fef2f2;
  --amber:#d97706;
  --shadow:0 1px 2px rgba(16,24,40,.04), 0 8px 24px rgba(16,24,40,.06);
  --radius:16px;
  --radius-sm:10px;
}
*{box-sizing:border-box}
html,body{margin:0;padding:0}
body{
  font-family:"Inter",system-ui,-apple-system,"Segoe UI",Roboto,Arial,sans-serif;
  background:var(--bg);
  color:var(--ink);
  line-height:1.55;
  -webkit-font-smoothing:antialiased;
}
a{color:var(--brand);text-decoration:none}
.container{max-width:840px;margin:0 auto;padding:24px 20px 64px}
.container-wide{max-width:1100px;margin:0 auto;padding:24px 20px 64px}

/* ---------- Top bar ---------- */
.topbar{
  position:sticky;top:0;z-index:30;
  background:rgba(255,255,255,.85);
  backdrop-filter:saturate(180%) blur(10px);
  border-bottom:1px solid var(--line);
}
.topbar .inner{max-width:1100px;margin:0 auto;padding:12px 20px;display:flex;align-items:center;gap:12px}
.brand{display:flex;align-items:center;gap:10px;font-weight:700;letter-spacing:-.01em}
.brand .brand-logo{height:30px;width:auto;display:block}
.brand .sep{width:1px;height:22px;background:var(--line)}
.brand .crumb{font-weight:600;color:var(--muted);font-size:12px}
.topbar .spacer{flex:1}
.pill{font-size:12px;color:var(--muted);background:var(--brand-50);border:1px solid var(--line);padding:5px 10px;border-radius:999px;font-weight:600}
a.pill{transition:background .15s,color .15s}
a.pill:hover{background:var(--brand);color:#fff;border-color:var(--brand)}

/* Brand banner (làm nổi bật logo trên trang giới thiệu) */
.brand-banner{
  display:flex;flex-direction:column;align-items:center;gap:12px;text-align:center;
  margin:-28px -28px 22px;padding:30px 24px 26px;
  background:radial-gradient(120% 120% at 50% 0%, #ffffff 0%, #eef4ff 60%, #e7efff 100%);
  border-bottom:1px solid var(--line);
  border-radius:var(--radius) var(--radius) 0 0;
}
.brand-banner img{height:92px;width:auto;filter:drop-shadow(0 6px 14px rgba(20,150,160,.18))}
.brand-banner .site-link{
  display:inline-flex;align-items:center;gap:6px;font-weight:700;font-size:13px;
  color:var(--brand-700);background:#fff;border:1px solid var(--line);
  padding:6px 14px;border-radius:999px;box-shadow:var(--shadow);
}
.brand-banner .site-link:hover{background:var(--brand);color:#fff;border-color:var(--brand)}
@media (max-width:640px){ .brand-banner{margin:-20px -20px 18px;padding:24px 16px} .brand-banner img{height:68px} }

/* ---------- Cards ---------- */
.card{
  background:var(--panel);
  border:1px solid var(--line);
  border-radius:var(--radius);
  box-shadow:var(--shadow);
  padding:28px;
}
.card + .card{margin-top:18px}

/* ---------- Hero / intro ---------- */
.hero h1{font-size:26px;margin:0 0 6px;letter-spacing:-.02em}
.hero p.lead{color:var(--muted);margin:0 0 20px;font-size:15px}
.meta-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:12px;margin:20px 0 8px}
.meta-grid .item{background:var(--brand-50);border:1px solid var(--line);border-radius:var(--radius-sm);padding:14px 16px}
.meta-grid .item .k{font-size:12px;color:var(--muted);font-weight:600}
.meta-grid .item .v{font-size:18px;font-weight:800;letter-spacing:-.02em}
.rules{margin:18px 0 0;padding:16px 18px;background:#fbfcff;border:1px dashed var(--line);border-radius:var(--radius-sm);color:var(--muted);font-size:14px}
.rules ul{margin:8px 0 0;padding-left:18px}
.rules li{margin:3px 0}

/* ---------- Form ---------- */
label.field{display:block;margin:16px 0 0;font-weight:600;font-size:14px}
label.field span.req{color:var(--red)}
input[type=text]{
  width:100%;margin-top:7px;padding:12px 14px;border:1px solid var(--line);
  border-radius:var(--radius-sm);font-size:15px;background:#fff;color:var(--ink);
  transition:border-color .15s, box-shadow .15s;
}
input[type=text]:focus{outline:none;border-color:var(--brand);box-shadow:0 0 0 4px var(--brand-50)}

/* ---------- Buttons ---------- */
.btn{
  display:inline-flex;align-items:center;justify-content:center;gap:8px;
  border:1px solid transparent;border-radius:var(--radius-sm);
  padding:12px 20px;font-size:15px;font-weight:700;cursor:pointer;
  transition:transform .04s, background .15s, box-shadow .15s;font-family:inherit;
}
.btn:active{transform:translateY(1px)}
.btn-primary{background:var(--brand);color:#fff}
.btn-primary:hover{background:var(--brand-700)}
.btn-ghost{background:#fff;border-color:var(--line);color:var(--ink)}
.btn-ghost:hover{background:#f8fafc}
.btn-lg{padding:14px 26px;font-size:16px}
.btn[disabled]{opacity:.5;cursor:not-allowed}
.btn-block{width:100%}

/* ---------- Quiz ---------- */
.progress-wrap{position:sticky;top:55px;z-index:20;background:var(--bg);padding:14px 0 10px}
.progress-head{display:flex;justify-content:space-between;align-items:center;margin-bottom:8px;font-size:13px;color:var(--muted);font-weight:600}
.progress-bar{height:8px;border-radius:999px;background:#e6eaf3;overflow:hidden}
.progress-bar > i{display:block;height:100%;width:0;background:linear-gradient(90deg,var(--brand),#7c3aed);transition:width .25s}
.timer{font-variant-numeric:tabular-nums;font-weight:700;color:var(--ink);background:#fff;border:1px solid var(--line);border-radius:999px;padding:4px 12px}
.timer.warn{color:var(--red);border-color:#fcd9d9;background:var(--red-50)}

.q-card{margin-top:16px}
.q-top{display:flex;align-items:center;gap:10px;margin-bottom:10px}
.q-index{font-weight:800;color:var(--brand)}
.tag-type{font-size:11px;font-weight:700;text-transform:uppercase;letter-spacing:.04em;color:var(--brand-700);background:var(--brand-50);border:1px solid var(--line);padding:3px 9px;border-radius:999px}
.tag-sec{font-size:11px;font-weight:600;color:var(--muted);background:#f1f5f9;padding:3px 9px;border-radius:999px}
.q-text{font-size:18px;font-weight:700;margin:6px 0 18px;letter-spacing:-.01em}
.q-hint{font-size:12.5px;color:var(--muted);margin:-12px 0 16px}

.options{display:flex;flex-direction:column;gap:10px}
.opt{
  display:flex;align-items:flex-start;gap:12px;padding:14px 16px;
  border:1.5px solid var(--line);border-radius:12px;cursor:pointer;background:#fff;
  transition:border-color .12s, background .12s;
}
.opt:hover{border-color:#c7d2fe;background:#fafbff}
.opt.sel{border-color:var(--brand);background:var(--brand-50)}
.opt .mark{
  flex:0 0 22px;height:22px;border:1.5px solid #cbd5e1;border-radius:50%;
  display:grid;place-items:center;margin-top:1px;color:#fff;font-size:12px;font-weight:800;
}
.opt.multi .mark{border-radius:6px}
.opt.sel .mark{background:var(--brand);border-color:var(--brand)}
.opt .label{flex:1;font-size:15px}

.nav-row{display:flex;justify-content:space-between;gap:12px;margin-top:22px}
.dots{display:flex;flex-wrap:wrap;gap:6px;margin-top:18px;justify-content:center}
.dot{width:26px;height:26px;border-radius:7px;border:1px solid var(--line);background:#fff;font-size:12px;font-weight:700;color:var(--muted);cursor:pointer;display:grid;place-items:center}
.dot.answered{background:var(--brand-50);border-color:#c7d2fe;color:var(--brand-700)}
.dot.current{background:var(--brand);border-color:var(--brand);color:#fff}

/* ---------- Result ---------- */
.score-ring{display:grid;place-items:center;width:160px;height:160px;border-radius:50%;margin:6px auto 14px;
  background:conic-gradient(var(--ring-color) calc(var(--pct)*1%), #eef1f7 0);}
.score-ring .inner{width:124px;height:124px;border-radius:50%;background:#fff;display:grid;place-items:center;text-align:center}
.score-ring .pct{font-size:32px;font-weight:800;letter-spacing:-.02em}
.score-ring .pl{font-size:12px;color:var(--muted);font-weight:600}
.verdict{text-align:center;font-size:20px;font-weight:800;margin:4px 0}
.verdict.pass{color:var(--green)}
.verdict.fail{color:var(--red)}
.stat-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:12px;margin:18px 0}
.stat{background:#fbfcff;border:1px solid var(--line);border-radius:var(--radius-sm);padding:14px;text-align:center}
.stat .n{font-size:24px;font-weight:800}
.stat .l{font-size:12px;color:var(--muted);font-weight:600}
.stat.ok .n{color:var(--green)} .stat.no .n{color:var(--red)}
.submit-state{font-size:13px;text-align:center;margin-top:10px;color:var(--muted)}

/* ---------- Review ---------- */
.review-item{border:1px solid var(--line);border-radius:12px;padding:18px;margin-top:14px;background:#fff}
.review-item.correct{border-left:4px solid var(--green)}
.review-item.wrong{border-left:4px solid var(--red)}
.rev-head{display:flex;align-items:center;gap:8px;margin-bottom:8px}
.badge{font-size:11px;font-weight:800;padding:3px 10px;border-radius:999px}
.badge.ok{background:var(--green-50);color:var(--green)}
.badge.no{background:var(--red-50);color:var(--red)}
.rev-q{font-weight:700;margin:4px 0 12px}
.rev-opt{padding:9px 12px;border-radius:8px;font-size:14px;margin:6px 0;border:1px solid transparent;display:flex;gap:8px;align-items:flex-start}
.rev-opt.ans{background:var(--green-50);border-color:#bbf7d0}
.rev-opt.you-wrong{background:var(--red-50);border-color:#fecaca}
.rev-opt .ic{font-weight:800}
.rev-opt.ans .ic{color:var(--green)} .rev-opt.you-wrong .ic{color:var(--red)}
.explain{margin-top:12px;padding:12px 14px;background:var(--brand-50);border:1px solid #dbe4ff;border-radius:10px;font-size:14px;color:#1e293b}
.explain b{color:var(--brand-700)}

/* ---------- Misc ---------- */
/* ---------- Song ngữ VI/EN ---------- */
.t-vi,.t-en{display:block}
body.lang-vi .t-en{display:none}
body.lang-en .t-vi{display:none}
/* Chế độ Song ngữ: EN là dòng phụ, nhạt + nghiêng */
body.lang-both .q-text .t-en,
body.lang-both .opt .label .t-en,
body.lang-both .rev-q .t-en,
body.lang-both .rev-opt .t-en,
body.lang-both .explain .t-en,
body.lang-both .q-hint .t-en,
body.lang-both .hero h1 .t-en,
body.lang-both .lead .t-en{
  color:var(--muted);font-weight:500;font-style:italic;font-size:.9em;margin-top:3px;
}
body.lang-both .hero h1 .t-en{font-size:.62em;font-weight:600}
/* Chip nhỏ (loại câu / section): luôn 1 dòng, inline; mặc định hiện VI, chỉ EN-mode hiện EN */
.tag-type .t-vi,.tag-type .t-en,.tag-sec .t-vi,.tag-sec .t-en,.q-index .t-vi,.q-index .t-en{display:inline}
.tag-type .t-en,.tag-sec .t-en,.q-index .t-en,.timer-x{display:none}
body.lang-en .tag-type .t-vi,body.lang-en .tag-sec .t-vi,body.lang-en .q-index .t-vi{display:none}
body.lang-en .tag-type .t-en,body.lang-en .tag-sec .t-en,body.lang-en .q-index .t-en{display:inline}
.p-label .t-vi,.p-label .t-en,#p-label .t-vi,#p-label .t-en{display:inline}
#p-label .t-en{display:none}
body.lang-en #p-label .t-vi{display:none}
body.lang-en #p-label .t-en{display:inline}
.verdict .t-vi,.verdict .t-en{display:block}
.badge .t-vi,.badge .t-en{display:inline}
.badge .t-en{display:none}
body.lang-en .badge .t-vi{display:none}
body.lang-en .badge .t-en{display:inline}
.btn .t-vi,.btn .t-en{display:inline}
.btn .t-en{display:none}
body.lang-en .btn .t-vi{display:none}
body.lang-en .btn .t-en{display:inline}
body.lang-both .btn .t-en{display:inline}
body.lang-both .btn .t-en::before{content:" / "}

/* Nút chuyển ngôn ngữ */
.lang-toggle{display:inline-flex;border:1px solid var(--line);border-radius:999px;overflow:hidden;background:#fff}
.lang-toggle button{border:none;background:#fff;padding:6px 13px;font-size:12px;font-weight:700;cursor:pointer;color:var(--muted);font-family:inherit}
.lang-toggle button + button{border-left:1px solid var(--line)}
.lang-toggle button.active{background:var(--brand);color:#fff}
.lang-row{display:flex;align-items:center;gap:10px;justify-content:center;margin:18px 0 2px;flex-wrap:wrap}
.lang-row .lbl{font-size:12.5px;color:var(--muted);font-weight:600}
.quiz-lang{display:flex;justify-content:flex-end;margin-bottom:-6px}

.center{text-align:center}
.muted{color:var(--muted)}
.err{color:var(--red);font-size:13px;margin-top:8px}
.footer{text-align:center;color:var(--muted);font-size:12px;margin-top:26px}
.hidden{display:none !important}

/* ---------- Admin table ---------- */
table{width:100%;border-collapse:collapse;font-size:14px}
th,td{text-align:left;padding:11px 12px;border-bottom:1px solid var(--line)}
th{font-size:12px;text-transform:uppercase;letter-spacing:.03em;color:var(--muted);background:#fbfcff}
tr:hover td{background:#fafbff}
.chip{font-size:12px;font-weight:700;padding:3px 9px;border-radius:999px}
.chip.pass{background:var(--green-50);color:var(--green)}
.chip.fail{background:var(--red-50);color:var(--red)}
.toolbar{display:flex;gap:10px;flex-wrap:wrap;align-items:center;margin-bottom:16px}
.kpi-grid{display:grid;grid-template-columns:repeat(4,1fr);gap:12px;margin-bottom:18px}
.kpi{background:var(--panel);border:1px solid var(--line);border-radius:var(--radius-sm);padding:16px;box-shadow:var(--shadow)}
.kpi .n{font-size:26px;font-weight:800;letter-spacing:-.02em}
.kpi .l{font-size:12px;color:var(--muted);font-weight:600}

@media (max-width:640px){
  .meta-grid,.stat-grid{grid-template-columns:repeat(3,1fr)}
  .kpi-grid{grid-template-columns:repeat(2,1fr)}
  .card{padding:20px}
  .q-text{font-size:17px}
  .container,.container-wide{padding:16px 14px 56px}
}