:root {
  --bg: #f4f6f8; --card: #ffffff; --ink: #1d2733; --muted: #5f6b7a; --line: #dde3ea;
  --brand: #12668f; --brand-ink: #ffffff; --ok: #1d7f45; --warn: #b26a00; --bad: #b42318;
  --sel: #e6f2f8; --radius: 10px;
}
* { box-sizing: border-box; }
html, body { margin: 0; background: var(--bg); color: var(--ink); font: 16px/1.5 "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif; }
a { color: var(--brand); }
h1, h2, h3 { line-height: 1.25; margin: 0 0 .6em; }
h1 { font-size: 1.5rem; } h2 { font-size: 1.2rem; } h3 { font-size: 1.05rem; }
.wrap { max-width: 1100px; margin: 0 auto; padding: 16px; }
.narrow { max-width: 440px; }
.card { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); padding: 20px; margin-bottom: 16px; }
.topbar { background: var(--brand); color: var(--brand-ink); }
.topbar .wrap { display: flex; align-items: center; gap: 16px; padding-top: 10px; padding-bottom: 10px; }
.topbar .brand { font-weight: 700; }
.topbar .sp { flex: 1; }
.topbar button { background: transparent; color: #fff; border: 1px solid rgba(255,255,255,.6); }
label { display: block; font-weight: 600; margin: 10px 0 4px; font-size: .95rem; }
input[type=text], input[type=password], input[type=number], input[type=datetime-local], select, textarea {
  width: 100%; padding: 9px 11px; border: 1px solid #c4cdd7; border-radius: 8px; font: inherit; background: #fff; color: inherit;
}
textarea { min-height: 140px; resize: vertical; }
button, .btn { display: inline-block; padding: 9px 16px; border-radius: 8px; border: 1px solid var(--brand); background: var(--brand); color: #fff; font: inherit; font-weight: 600; cursor: pointer; text-decoration: none; }
button.secondary, .btn.secondary { background: #fff; color: var(--brand); }
button.danger { background: var(--bad); border-color: var(--bad); }
button.small { padding: 4px 10px; font-size: .88rem; font-weight: 500; }
button:disabled { opacity: .55; cursor: not-allowed; }
.row { display: flex; gap: 12px; flex-wrap: wrap; align-items: flex-end; }
.row > * { flex: 1 1 180px; }
.muted { color: var(--muted); }
.err { color: var(--bad); font-weight: 600; }
.okc { color: var(--ok); font-weight: 600; }
.tag { display: inline-block; padding: 1px 8px; border-radius: 999px; font-size: .82rem; border: 1px solid var(--line); background: #f7f9fb; }
.tag.ok { color: var(--ok); border-color: #b7dfc6; background: #eef8f2; }
.tag.warn { color: var(--warn); border-color: #f0d29b; background: #fff7e8; }
.tag.bad { color: var(--bad); border-color: #f2b8b5; background: #fdeeee; }
table.list { width: 100%; border-collapse: collapse; font-size: .94rem; }
table.list th, table.list td { padding: 7px 8px; border-bottom: 1px solid var(--line); text-align: left; vertical-align: top; }
table.list th { background: #f0f3f6; font-weight: 600; position: sticky; top: 0; }
.tablewrap { overflow-x: auto; }
.tabs { display: flex; gap: 6px; flex-wrap: wrap; margin-bottom: 14px; }
.tabs button { background: #fff; color: var(--ink); border-color: var(--line); }
.tabs button.on { background: var(--brand); color: #fff; border-color: var(--brand); }
.hidden { display: none !important; }
.qhtml table { border-collapse: collapse; margin: 8px 0; max-width: 100%; }
.qhtml td, .qhtml th { border: 1px solid #9aa6b2; padding: 3px 6px; }
.qhtml img { max-width: 100%; height: auto; }
.qhtml p { margin: .3em 0; }
dialog { border: 1px solid var(--line); border-radius: var(--radius); padding: 20px; max-width: 900px; width: calc(100% - 32px); }
dialog::backdrop { background: rgba(0,0,0,.35); }

/* ---------- trang làm bài ---------- */
body.exam { user-select: none; -webkit-user-select: none; }
body.exam textarea, body.exam input[type=text] { user-select: text; -webkit-user-select: text; }
.examhead { position: sticky; top: 0; z-index: 20; background: #fff; border-bottom: 1px solid var(--line); }
.examhead .wrap { display: flex; align-items: center; gap: 14px; padding-top: 8px; padding-bottom: 8px; flex-wrap: wrap; }
.timer { font-variant-numeric: tabular-nums; font-size: 1.35rem; font-weight: 700; color: var(--brand); }
.timer.low { color: var(--bad); }
.save { font-size: .85rem; }
.examgrid { display: grid; grid-template-columns: 1fr 230px; gap: 16px; align-items: start; }
.nav { position: sticky; top: 70px; }
.nav .grid { display: grid; grid-template-columns: repeat(5, 1fr); gap: 6px; }
.nav .grid button { padding: 6px 0; background: #fff; color: var(--ink); border-color: var(--line); font-weight: 600; }
.nav .grid button.done { background: var(--sel); border-color: var(--brand); color: var(--brand); }
.q { scroll-margin-top: 80px; }
.q .qno { font-weight: 700; color: var(--brand); }
.partttl { font-weight: 700; margin: 6px 0 12px; }
.opt { display: flex; gap: 10px; align-items: flex-start; padding: 8px 10px; border: 1px solid var(--line); border-radius: 8px; margin: 6px 0; cursor: pointer; }
.opt:hover { background: #f7fafc; }
.opt.sel { background: var(--sel); border-color: var(--brand); }
.opt .lbl { font-weight: 700; min-width: 1.4em; }
.ds { width: 100%; border-collapse: collapse; }
.ds td { border-bottom: 1px solid var(--line); padding: 8px 4px; vertical-align: top; }
.ds td.ch { white-space: nowrap; width: 1%; }
.ds label { display: inline-flex; align-items: center; gap: 4px; margin: 0 6px; font-weight: 600; }
.watermark { position: fixed; inset: 0; pointer-events: none; z-index: 10; opacity: .045; font-size: 22px; font-weight: 700; color: #000;
  display: flex; flex-wrap: wrap; align-content: space-around; justify-content: space-around; transform: rotate(-24deg) scale(1.4); overflow: hidden; }
.overlay { position: fixed; inset: 0; background: rgba(20,30,40,.92); color: #fff; z-index: 100; display: flex; align-items: center; justify-content: center; padding: 20px; text-align: center; }
.overlay .box { max-width: 520px; }
.overlay h2 { color: #fff; }
.overlay button { margin-top: 14px; background: #fff; color: var(--brand); border-color: #fff; }
@media (max-width: 820px) {
  .examgrid { grid-template-columns: 1fr; }
  .nav { position: static; order: -1; }
  .nav .grid { grid-template-columns: repeat(8, 1fr); }
}
@media print { body.exam * { display: none !important; } }