:root {
  --bg: #f1f5f9;
  --panel: #ffffff;
  --ink: #0f172a;
  --muted: #64748b;
  --line: #e2e8f0;
  --brand: #1d4ed8;
  --brand2: #0891b2;
  --green: #16a34a;
  --red: #dc2626;
  --amber: #d97706;
  --purple: #7c3aed;
  --shadow: 0 1px 2px rgba(15, 23, 42, .06), 0 8px 24px rgba(15, 23, 42, .06);
}
* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }
body {
  font-family: "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  background: var(--bg); color: var(--ink); line-height: 1.5;
}
a { color: var(--brand); text-decoration: none; }
button { font-family: inherit; }
.hidden { display: none !important; }

.topbar {
  position: sticky; top: 0; z-index: 30;
  background: linear-gradient(100deg, #1e3a8a, #1d4ed8 55%, #0891b2);
  color: #fff; box-shadow: var(--shadow);
}
.topbar-inner {
  max-width: 1180px; margin: 0 auto; padding: 10px 16px;
  display: flex; align-items: center; gap: 16px; flex-wrap: wrap;
}
.brand { display: flex; align-items: center; gap: 10px; font-weight: 700; font-size: 17px; }
.brand .logo {
  width: 34px; height: 34px; border-radius: 9px; background: #fff; color: #1d4ed8;
  display: grid; place-items: center; font-size: 13px; font-weight: 800; letter-spacing: .5px;
}
.brand small { display: block; font-weight: 400; font-size: 11px; opacity: .85; }
nav.mainnav { display: flex; gap: 4px; margin-left: auto; flex-wrap: wrap; }
nav.mainnav a {
  color: #e0e7ff; padding: 7px 12px; border-radius: 8px; font-size: 14px;
}
nav.mainnav a:hover { background: rgba(255, 255, 255, .14); color: #fff; }
nav.mainnav a.active { background: rgba(255, 255, 255, .22); color: #fff; font-weight: 600; }

main { max-width: 1180px; margin: 0 auto; padding: 20px 16px 64px; }
.page-title { font-size: 22px; margin: 0 0 4px; }
.page-sub { color: var(--muted); margin: 0 0 18px; font-size: 14px; }

.grid { display: grid; gap: 14px; }
.g4 { grid-template-columns: repeat(4, 1fr); }
.g3 { grid-template-columns: repeat(3, 1fr); }
.g2 { grid-template-columns: repeat(2, 1fr); }
@media (max-width: 900px) { .g4 { grid-template-columns: repeat(2, 1fr); } .g3 { grid-template-columns: repeat(2, 1fr); } }
@media (max-width: 620px) { .g4, .g3, .g2 { grid-template-columns: 1fr; } }

.card {
  background: var(--panel); border: 1px solid var(--line); border-radius: 14px;
  padding: 16px; box-shadow: var(--shadow);
}
.stat { display: flex; flex-direction: column; gap: 2px; }
.stat .k { font-size: 26px; font-weight: 800; }
.stat .l { font-size: 13px; color: var(--muted); }
.stat .i { font-size: 12px; }

.section-head { display: flex; align-items: center; gap: 10px; margin: 26px 0 12px; }
.section-head h2 { font-size: 18px; margin: 0; }
.pill { font-size: 11px; padding: 2px 9px; border-radius: 999px; background: #eef2ff; color: #3730a3; font-weight: 600; }

.topic-card { cursor: pointer; transition: transform .12s, box-shadow .12s; }
.topic-card:hover { transform: translateY(-2px); box-shadow: 0 10px 26px rgba(15, 23, 42, .12); }
.topic-card h3 { margin: 0 0 6px; font-size: 15px; }
.topic-card .meta { font-size: 12px; color: var(--muted); }
.bar { height: 6px; border-radius: 4px; background: #e2e8f0; overflow: hidden; margin-top: 10px; }
.bar > span { display: block; height: 100%; background: var(--green); }

.btn {
  display: inline-flex; align-items: center; gap: 7px; justify-content: center;
  border: 1px solid transparent; border-radius: 10px; padding: 9px 15px;
  font-size: 14px; font-weight: 600; cursor: pointer; background: var(--brand); color: #fff;
}
.btn:hover { filter: brightness(1.06); }
.btn.ghost { background: #fff; color: var(--ink); border-color: var(--line); }
.btn.green { background: var(--green); }
.btn.red { background: var(--red); }
.btn.amber { background: var(--amber); }
.btn.purple { background: var(--purple); }
.btn.sm { padding: 6px 11px; font-size: 13px; }
.btn:disabled { opacity: .5; cursor: not-allowed; }
.btn-row { display: flex; gap: 10px; flex-wrap: wrap; }

.notes h3 { font-size: 15px; margin: 18px 0 8px; }
.notes ul { margin: 0; padding-left: 20px; }
.notes li { margin-bottom: 6px; font-size: 14px; }
.formula { display: flex; gap: 8px; flex-wrap: wrap; margin-top: 10px; }
.formula code {
  background: #eef2ff; color: #3730a3; padding: 4px 10px; border-radius: 8px; font-size: 13px;
}
.crumb { font-size: 13px; color: var(--muted); margin-bottom: 10px; }
.crumb a { color: var(--brand); }

/* ---- test layout ---- */
.test-wrap { display: grid; grid-template-columns: 1fr 264px; gap: 16px; align-items: start; }
@media (max-width: 860px) { .test-wrap { grid-template-columns: 1fr; } }
.test-top {
  display: flex; align-items: center; gap: 12px; flex-wrap: wrap;
  background: var(--panel); border: 1px solid var(--line); border-radius: 14px; padding: 12px 16px;
  margin-bottom: 14px; box-shadow: var(--shadow);
}
.test-top .tname { font-weight: 700; }
.test-top .spacer { margin-left: auto; }
.timer { font-variant-numeric: tabular-nums; font-weight: 800; font-size: 18px; padding: 4px 12px; border-radius: 8px; background: #eef2ff; color: #1e3a8a; }
.timer.warn { background: #fef3c7; color: #92400e; }
.timer.danger { background: #fee2e2; color: #991b1b; animation: pulse 1s infinite; }
@keyframes pulse { 50% { opacity: .55; } }

.qcard { background: var(--panel); border: 1px solid var(--line); border-radius: 14px; padding: 20px; box-shadow: var(--shadow); }
.qnum { font-size: 12px; font-weight: 700; color: var(--brand); letter-spacing: .4px; text-transform: uppercase; }
.qtext { font-size: 16px; margin: 10px 0 16px; white-space: pre-wrap; }
.qtext table { border-collapse: collapse; margin-top: 10px; }
.qtext table td, .qtext table th { border: 1px solid var(--line); padding: 5px 12px; font-size: 14px; }
.qtext table th { background: #f8fafc; }
.options { display: flex; flex-direction: column; gap: 10px; }
.opt {
  display: flex; align-items: flex-start; gap: 10px; border: 1px solid var(--line);
  border-radius: 10px; padding: 11px 14px; cursor: pointer; background: #fff; font-size: 15px; text-align: left;
}
.opt:hover { border-color: #93c5fd; background: #f8fbff; }
.opt .idx {
  width: 24px; height: 24px; border-radius: 50%; border: 1px solid var(--line);
  display: grid; place-items: center; font-size: 12px; font-weight: 700; flex: none; background: #f8fafc;
}
.opt.sel { border-color: var(--brand); background: #eff6ff; }
.opt.sel .idx { background: var(--brand); color: #fff; border-color: var(--brand); }
.opt.correct { border-color: var(--green); background: #f0fdf4; }
.opt.correct .idx { background: var(--green); color: #fff; border-color: var(--green); }
.opt.wrong { border-color: var(--red); background: #fef2f2; }
.opt.wrong .idx { background: var(--red); color: #fff; border-color: var(--red); }
.explain {
  margin-top: 16px; border-left: 4px solid var(--amber); background: #fffbeb;
  padding: 12px 14px; border-radius: 0 10px 10px 0; font-size: 14px;
}
.explain b { color: #92400e; }

/* palette */
.palette { background: var(--panel); border: 1px solid var(--line); border-radius: 14px; padding: 14px; box-shadow: var(--shadow); position: sticky; top: 76px; }
.palette h4 { margin: 0 0 10px; font-size: 13px; text-transform: uppercase; letter-spacing: .5px; color: var(--muted); }
.pgrid { display: grid; grid-template-columns: repeat(5, 1fr); gap: 7px; }
.pal {
  aspect-ratio: 1; border-radius: 8px; border: 1px solid var(--line); background: #f8fafc;
  font-size: 13px; font-weight: 700; cursor: pointer; color: #475569;
}
.pal.answered { background: var(--green); border-color: var(--green); color: #fff; }
.pal.marked { background: var(--purple); border-color: var(--purple); color: #fff; }
.pal.marked.answered { background: var(--purple); color: #fff; box-shadow: inset 0 -5px 0 var(--green); }
.pal.notans { background: #fee2e2; border-color: #fecaca; color: #991b1b; }
.pal.current { outline: 3px solid #1d4ed8; outline-offset: 1px; }
.legend { margin-top: 12px; font-size: 12px; color: var(--muted); display: flex; flex-direction: column; gap: 5px; }
.legend i { display: inline-block; width: 12px; height: 12px; border-radius: 3px; margin-right: 7px; vertical-align: -2px; }

.result-hero { text-align: center; padding: 8px 0 4px; }
.result-hero .big { font-size: 40px; font-weight: 800; }
.result-hero .sub { color: var(--muted); }
table.review { width: 100%; border-collapse: collapse; font-size: 14px; }
table.review th, table.review td { border-bottom: 1px solid var(--line); padding: 9px 8px; text-align: left; }
table.review th { background: #f8fafc; font-size: 12px; text-transform: uppercase; letter-spacing: .4px; color: var(--muted); }
.tag { font-size: 11px; padding: 2px 8px; border-radius: 999px; font-weight: 700; }
.tag.g { background: #dcfce7; color: #166534; }
.tag.r { background: #fee2e2; color: #991b1b; }
.tag.a { background: #fef3c7; color: #92400e; }
.review-q { border: 1px solid var(--line); border-radius: 12px; padding: 14px; margin-bottom: 12px; background: #fff; }
.review-q .qh { font-size: 12px; color: var(--muted); display: flex; gap: 10px; align-items: center; margin-bottom: 6px; }
.review-q .qt { white-space: pre-wrap; font-size: 15px; }

.empty { text-align: center; color: var(--muted); padding: 40px 10px; }
.flex { display: flex; gap: 10px; align-items: center; flex-wrap: wrap; }
.muted { color: var(--muted); }
.small { font-size: 12px; }
.mt { margin-top: 14px; }
.mb { margin-bottom: 14px; }
.right { text-align: right; }
select, input[type=number] { padding: 8px 10px; border: 1px solid var(--line); border-radius: 9px; font-size: 14px; font-family: inherit; }
.toast {
  position: fixed; bottom: 20px; left: 50%; transform: translateX(-50%);
  background: #0f172a; color: #fff; padding: 10px 18px; border-radius: 10px; font-size: 14px; z-index: 100;
  box-shadow: var(--shadow);
}
.modal-bg { position: fixed; inset: 0; background: rgba(15, 23, 42, .5); display: grid; place-items: center; z-index: 90; padding: 16px; }
.modal { background: #fff; border-radius: 14px; padding: 20px; max-width: 420px; width: 100%; }