:root { --accent: #0f766e; --accent-dark: #115e59; --ink: #1a1d21; --muted: #5b6470; --line: #dfe3e8; --panel: #f1f3f4; --danger: #b3261e; --warn-bg: #fff7e0; --warn-line: #e3c878; --good: #146c2e; }
* { box-sizing: border-box; }
body { margin: 0; color: var(--ink); font-family: system-ui, -apple-system, "Segoe UI", Roboto, sans-serif; font-size: 16px; line-height: 1.55; background: #fff; padding-bottom: 76px; }
.wrap { max-width: 760px; margin: 0 auto; padding: 0 12px; }
.banner { background: var(--warn-bg); border-bottom: 1px solid var(--warn-line); padding: 8px 12px; font-size: 14px; }
.topbar { border-bottom: 1px solid var(--line); padding: 10px 0; background: #fff; position: sticky; top: 0; z-index: 5; }
.brand { font-weight: 700; font-size: 18px; }
.tokenrow { display: flex; gap: 8px; align-items: center; margin: 8px 0; }
.tokenrow label { font-size: 13px; color: var(--muted); }
.userbox { display: flex; gap: 8px; align-items: center; font-size: 13px; }
.userbox #username { font-weight: 700; }
.login { max-width: 420px; margin: 24px auto; }
.login input { width: 100%; box-sizing: border-box; padding: 10px; margin: 6px 0; font-size: 15px; border: 1px solid var(--line); border-radius: 6px; }
.tabs { display: flex; gap: 6px; margin-bottom: 10px; }
table.grid { width: 100%; border-collapse: collapse; font-size: 13px; }
table.grid th, table.grid td { text-align: left; padding: 6px 8px; border-bottom: 1px solid var(--line); vertical-align: top; }
table.grid tr:hover td { background: #f4faf9; }
.formgrid { display: grid; gap: 8px; }
.formgrid label { font-size: 13px; font-weight: 700; }
.formgrid input[type="text"], .formgrid textarea, .formgrid select { width: 100%; box-sizing: border-box; padding: 8px; font-size: 14px; border: 1px solid var(--line); border-radius: 6px; font-family: inherit; }
.formgrid textarea { min-height: 64px; }
.statgrid { display: grid; grid-template-columns: repeat(auto-fit, minmax(140px, 1fr)); gap: 8px; margin: 10px 0; }
.statgrid .stat { border: 1px solid var(--line); border-radius: 6px; padding: 8px; }
.statgrid .stat b { display: block; font-size: 20px; }
.admin-tag { font-size: 12px; font-weight: 700; letter-spacing: 1px; background: #6d28d9; color: #fff; border-radius: 4px; padding: 2px 8px; vertical-align: middle; }
body.is-admin .topbar { background: #232a35; color: #f3f4f6; border-bottom-color: #232a35; }
body.is-admin .brand::after { content: ' · Quản trị'; font-weight: 400; font-size: 14px; color: #c4b5fd; }
body.is-admin .userbox #username { color: #f3f4f6; }
body.is-admin button.primary { background: #6d28d9; border-color: #6d28d9; }
body.is-admin .bottomnav button.on { color: #6d28d9; }
body.is-admin .subjects button.on { background: #6d28d9; border-color: #6d28d9; }
.subjects { display: flex; gap: 8px; flex-wrap: wrap; }
.subjects button { border: 1px solid var(--line); background: #fff; border-radius: 20px; padding: 8px 14px; font-size: 15px; min-height: 40px; }
.subjects button.on { background: var(--accent); border-color: var(--accent); color: #fff; }
button { font-size: 16px; min-height: 44px; padding: 10px 16px; border-radius: 8px; border: 1px solid var(--line); background: #fff; color: var(--ink); }
button.primary { background: var(--accent); border-color: var(--accent); color: #fff; }
button.primary:active { background: var(--accent-dark); }
button:disabled { opacity: .55; }
button.small { min-height: 36px; font-size: 14px; padding: 6px 12px; }
.bottomnav { position: fixed; bottom: 0; left: 0; right: 0; display: flex; border-top: 1px solid var(--line); background: #fff; z-index: 5; }
.bottomnav button { flex: 1; border: 0; border-radius: 0; min-height: 56px; font-size: 14px; color: var(--muted); }
.bottomnav button.on { color: var(--accent-dark); font-weight: 700; }
h2 { font-size: 20px; margin: 18px 0 8px; }
h3 { font-size: 17px; margin: 14px 0 6px; }
.muted { color: var(--muted); font-size: 14px; }
.badge { display: inline-block; font-size: 12px; border: 1px solid var(--line); border-radius: 4px; padding: 1px 8px; margin-left: 6px; color: var(--muted); }
.badge.demo { border-color: var(--warn-line); background: var(--warn-bg); color: #7a5b00; }
.badge.ok { border-color: var(--good); background: #e9f5ec; color: var(--good); }
.qcard { border: 1px solid var(--line); border-radius: 8px; padding: 12px; margin: 12px 0; }
.passage { background: var(--panel); border-radius: 6px; padding: 10px 12px; margin-bottom: 10px; font-size: 15px; }
.stem { font-size: 17px; margin: 6px 0 10px; }
.opts { display: grid; gap: 8px; margin: 10px 0; }
.opt { text-align: left; border: 1px solid var(--line); background: #fff; }
.opt .k { display: inline-block; min-width: 26px; font-weight: 700; }
.opt.right { border-color: var(--good); background: #e9f5ec; }
.opt.wrong { border-color: var(--danger); background: #fdecea; }
.tfrow { border: 1px solid var(--line); border-radius: 6px; padding: 8px; background: #fff; }
.tfrow.right { border-color: var(--good); background: #e9f5ec; }
.tfrow.wrong { border-color: var(--danger); background: #fdecea; }
.tfrow .actions { margin-top: 6px; }
button.small.on { border-color: var(--accent); background: #e6f4f2; }
.shortin { width: 100%; box-sizing: border-box; padding: 10px; font-size: 16px; border: 1px solid var(--line); border-radius: 6px; }
.result { font-weight: 700; margin: 10px 0; }
.result.ok { color: var(--good); } .result.bad { color: var(--danger); }
.steps { margin: 10px 0; border-top: 1px dashed var(--line); }
.step { border-bottom: 1px dashed var(--line); padding: 8px 0; }
.step > button { width: 100%; text-align: left; border: 0; padding: 8px 4px; min-height: 44px; font-weight: 600; }
.stepbody { padding: 2px 4px 8px; font-size: 15px; }
.stepbody dt { font-weight: 600; font-size: 13px; color: var(--muted); margin-top: 6px; }
.stepbody dd { margin: 2px 0 0; }
.actions { display: flex; gap: 8px; flex-wrap: wrap; margin: 12px 0; }
.selfopts { display: grid; gap: 8px; margin: 10px 0; }
.selfopts button { text-align: left; }
.selfopts button.on { border-color: var(--accent); background: #e6f4f2; }
table.grid { border-collapse: collapse; width: 100%; font-size: 14px; margin: 8px 0; }
table.grid th, table.grid td { border: 1px solid var(--line); padding: 6px 8px; text-align: left; }
.prog { height: 8px; background: var(--panel); border-radius: 4px; overflow: hidden; margin: 8px 0; }
.prog > div { height: 100%; background: var(--accent); }
.timer { font-variant-numeric: tabular-nums; font-weight: 700; }
.timer.late { color: var(--danger); }
.examnav { display: flex; gap: 6px; flex-wrap: wrap; margin: 10px 0; }
.examnav button { min-width: 44px; min-height: 44px; padding: 6px; }
.examnav button.done { background: var(--panel); }
.examnav button.cur { border-color: var(--accent); }
.note { border: 1px solid var(--line); border-radius: 8px; padding: 10px 12px; margin: 8px 0; }
.note .meta { font-size: 13px; color: var(--muted); }
.filters { display: flex; gap: 8px; flex-wrap: wrap; margin: 10px 0; }
.filters select { font-size: 15px; padding: 8px; min-height: 44px; border: 1px solid var(--line); border-radius: 6px; background: #fff; }
.planmin { display: flex; gap: 8px; margin: 10px 0; }
.planmin button.on { background: var(--accent); color: #fff; border-color: var(--accent); }
.act { border: 1px solid var(--line); border-radius: 8px; padding: 10px 12px; margin: 8px 0; }
.act .why { font-size: 14px; color: var(--muted); }
math { font-size: 1.05em; }
math[display="block"] { margin: 8px 0; }
.math-error { background: #fdecea; color: var(--danger); border: 1px solid var(--danger); border-radius: 4px; padding: 0 6px; font-size: 13px; }
code.math-error { font-family: monospace; }
@media (min-width: 700px) { body { padding-bottom: 90px; } .bottomnav { max-width: 760px; margin: 0 auto; left: 0; right: 0; } }
@media (prefers-reduced-motion: reduce) { * { transition: none !important; animation: none !important; } }

/* First-run learning path: one obvious action, readable content, mobile-first. */
.welcome { margin: 20px 0 24px; padding: clamp(18px, 4vw, 28px); border: 1px solid #c9ded9; background: #f2faf7; border-radius: 16px; }
.welcome h2 { margin: 4px 0 8px; font-size: clamp(23px, 4vw, 30px); line-height: 1.22; }
.welcome p { margin: 0 0 14px; max-width: 60ch; }
.eyebrow { font-size: 11px; letter-spacing: .12em; font-weight: 800; color: #115e59; }
button.big-action { width: 100%; min-height: 52px; font-weight: 700; }
.act { padding: 16px; border-radius: 12px; }
.act .actions { margin-bottom: 0; }
button:focus-visible, input:focus-visible, select:focus-visible { outline: 3px solid #0f766e; outline-offset: 2px; }
@media(min-width:700px) { button.big-action { width: auto; min-width: 220px; } }