:root {
  --bg: #f4f5f7;
  --panel: #ffffff;
  --ink: #1c2333;
  --ink-soft: #5b6577;
  --line: #dfe3ea;
  --brand: #2f57d6;
  --brand-ink: #ffffff;
  --good: #1a7f45;
  --good-bg: #e7f5ec;
  --bad: #c02a37;
  --bad-bg: #fdecee;
  --warn: #9a6a00;
  --warn-bg: #fdf3df;
  --easy: #1a7f45;
  --medium: #9a6a00;
  --hard: #c02a37;
  --radius: 10px;
  --shadow: 0 1px 3px rgba(18, 25, 45, 0.08), 0 6px 20px rgba(18, 25, 45, 0.06);
  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #12151c;
    --panel: #1b1f29;
    --ink: #e8ebf2;
    --ink-soft: #9aa4b7;
    --line: #2c313d;
    --brand: #6a8bff;
    --brand-ink: #0d1017;
    --good: #4ccc82;
    --good-bg: #14301f;
    --bad: #ff7a86;
    --bad-bg: #331519;
    --warn: #ffc24d;
    --warn-bg: #322914;
    --easy: #4ccc82;
    --medium: #ffc24d;
    --hard: #ff7a86;
    --shadow: 0 1px 3px rgba(0, 0, 0, 0.4), 0 6px 20px rgba(0, 0, 0, 0.35);
  }
}

* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }
body {
  background: var(--bg);
  color: var(--ink);
  font-family: var(--font);
  font-size: 15px;
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
}
a { color: var(--brand); text-decoration: none; }
a:hover { text-decoration: underline; }
h1 { font-size: 1.5rem; margin: 0 0 .2em; }
h2 { font-size: 1.15rem; margin: 1.6em 0 .6em; }
h3 { font-size: 1rem; margin: 1.2em 0 .4em; }
p { margin: .5em 0; }
code { background: var(--bg); padding: .1em .35em; border-radius: 4px; font-size: .9em; }

/* top bar */
.topbar {
  position: sticky; top: 0; z-index: 30;
  display: flex; align-items: center; gap: 1.5rem;
  padding: .7rem 1.2rem;
  background: var(--panel);
  border-bottom: 1px solid var(--line);
}
.brand { font-weight: 700; font-size: 1.05rem; color: var(--ink); }
.brand span { color: var(--ink-soft); font-weight: 500; margin-left: .35em; }
.topbar nav { display: flex; gap: 1.1rem; margin-left: auto; flex-wrap: wrap; }
.topbar nav a { color: var(--ink-soft); font-weight: 500; }
.topbar nav a.active { color: var(--ink); }

.view { max-width: 1080px; margin: 0 auto; padding: 1.6rem 1.2rem 5rem; }
.loading { color: var(--ink-soft); padding: 3rem 0; text-align: center; }

/* cards + grid */
.panel {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 1.1rem 1.2rem;
}
.grid { display: grid; gap: 1rem; }
.grid.cols-2 { grid-template-columns: repeat(auto-fit, minmax(320px, 1fr)); }
.grid.cols-3 { grid-template-columns: repeat(auto-fit, minmax(240px, 1fr)); }
.grid.cols-4 { grid-template-columns: repeat(auto-fit, minmax(200px, 1fr)); }
.stack > * + * { margin-top: .8rem; }
.muted { color: var(--ink-soft); }
.small { font-size: .86rem; }
.right { text-align: right; }
.row { display: flex; gap: .6rem; align-items: center; flex-wrap: wrap; }
.spread { display: flex; justify-content: space-between; align-items: center; gap: 1rem; }

/* buttons */
button, .btn {
  font: inherit; cursor: pointer;
  border: 1px solid var(--line);
  background: var(--panel);
  color: var(--ink);
  padding: .5rem .9rem;
  border-radius: 8px;
  transition: filter .12s ease, background .12s ease;
}
button:hover, .btn:hover { filter: brightness(.97); text-decoration: none; }
button:disabled { opacity: .5; cursor: not-allowed; }
.btn-primary { background: var(--brand); border-color: var(--brand); color: var(--brand-ink); font-weight: 600; }
.btn-danger { color: var(--bad); border-color: var(--bad); }
.btn-ghost { background: transparent; }
.btn-sm { padding: .3rem .6rem; font-size: .85rem; }
.btn-block { display: block; width: 100%; text-align: center; }

/* pills / badges */
.pill {
  display: inline-block; padding: .12rem .55rem; border-radius: 999px;
  font-size: .76rem; font-weight: 600; border: 1px solid var(--line);
}
.pill.easy { color: var(--easy); border-color: var(--easy); }
.pill.medium { color: var(--medium); border-color: var(--medium); }
.pill.hard { color: var(--hard); border-color: var(--hard); }
.pill.good { color: var(--good); border-color: var(--good); background: var(--good-bg); }
.pill.bad { color: var(--bad); border-color: var(--bad); background: var(--bad-bg); }
.tag { display:inline-block; background: var(--bg); border:1px solid var(--line); border-radius:6px; padding:.05rem .45rem; font-size:.8rem; }

/* forms */
input[type="text"], input[type="password"], input[type="number"], select, textarea {
  font: inherit; color: var(--ink); background: var(--panel);
  border: 1px solid var(--line); border-radius: 8px; padding: .5rem .6rem; width: 100%;
}
label.field { display: block; margin: .8rem 0; }
label.field > span { display: block; font-weight: 600; margin-bottom: .25rem; font-size: .9rem; }

/* progress bar */
.bar { height: 8px; background: var(--bg); border-radius: 999px; overflow: hidden; border: 1px solid var(--line); }
.bar > i { display: block; height: 100%; background: var(--brand); width: 0; transition: width .3s ease; }

/* ---------- test runner ---------- */
.runner { display: grid; grid-template-columns: 1fr 320px; gap: 1.2rem; align-items: start; }
.runner .pages { min-width: 0; }
.runner .pages img {
  width: 100%; display: block; margin: 0 auto 10px;
  border: 1px solid var(--line); border-radius: 6px; background: #fff;
}
.runner .side {
  position: sticky; top: 66px;
  background: var(--panel); border: 1px solid var(--line);
  border-radius: var(--radius); box-shadow: var(--shadow);
  padding: .9rem; max-height: calc(100vh - 84px); display: flex; flex-direction: column;
}
.timer { font-size: 1.5rem; font-weight: 700; font-variant-numeric: tabular-nums; text-align: center; }
.timer.warn { color: var(--warn); }
.timer.danger { color: var(--bad); }
.grid-answers { overflow-y: auto; margin: .6rem -.2rem; padding: 0 .2rem; flex: 1; }
.qrow { display: flex; align-items: center; gap: .3rem; padding: .18rem 0; border-bottom: 1px dashed var(--line); }
.qrow > .n { width: 2.1rem; text-align: right; color: var(--ink-soft); font-variant-numeric: tabular-nums; font-size: .82rem; }
.qrow.flagged > .n::after { content: " ⚑"; color: var(--warn); }
.qrow .opt {
  width: 1.7rem; height: 1.7rem; border-radius: 50%; border: 1px solid var(--line);
  display: grid; place-items: center; font-size: .8rem; background: var(--panel); color: var(--ink-soft);
}
.qrow .opt.sel { background: var(--brand); border-color: var(--brand); color: var(--brand-ink); font-weight: 700; }
.qrow .flag { margin-left: auto; border: none; background: transparent; color: var(--ink-soft); padding: .1rem .3rem; }
.qrow.answered > .n { color: var(--ink); font-weight: 600; }

/* ---------- quiz (AI questions) ---------- */
.quiz .qcard { border: 1px solid var(--line); border-radius: var(--radius); padding: 1rem 1.1rem; background: var(--panel); box-shadow: var(--shadow); }
.quiz .passage { background: var(--bg); border: 1px solid var(--line); border-radius: 8px; padding: .7rem .8rem; white-space: pre-wrap; font-size: .95rem; }
.quiz .passage mark { background: var(--warn-bg); color: var(--ink); padding: 0 .15em; }
.quiz .choice {
  display: flex; gap: .6rem; align-items: flex-start; width: 100%; text-align: left;
  margin: .35rem 0; padding: .55rem .7rem; border-radius: 8px; border: 1px solid var(--line); background: var(--panel);
}
.quiz .choice .let { font-weight: 700; color: var(--ink-soft); }
.quiz .choice.sel { border-color: var(--brand); }
.quiz .choice.correct { border-color: var(--good); background: var(--good-bg); }
.quiz .choice.wrong { border-color: var(--bad); background: var(--bad-bg); }
.quiz .explain { margin-top: .6rem; padding: .6rem .75rem; border-left: 3px solid var(--brand); background: var(--bg); border-radius: 0 8px 8px 0; font-size: .92rem; }

/* results */
.scoreline { display: flex; gap: 1.4rem; flex-wrap: wrap; align-items: baseline; }
.scoreline .big { font-size: 2.6rem; font-weight: 800; line-height: 1; }
.wrong-item { border: 1px solid var(--line); border-radius: 8px; margin: .5rem 0; overflow: hidden; }
.wrong-item > summary { padding: .55rem .8rem; cursor: pointer; display: flex; gap: .6rem; align-items: center; flex-wrap: wrap; }
.wrong-item > summary::-webkit-details-marker { display: none; }
.wrong-item[open] > summary { border-bottom: 1px solid var(--line); background: var(--bg); }
.wrong-body { padding: .8rem; display: grid; gap: .8rem; grid-template-columns: minmax(0, 420px) 1fr; }
.wrong-body img { width: 100%; border: 1px solid var(--line); border-radius: 6px; }
@media (max-width: 720px) { .wrong-body { grid-template-columns: 1fr; } }

.mono { font-variant-numeric: tabular-nums; }
.divider { height: 1px; background: var(--line); margin: 1.4rem 0; }
.chip { display:inline-flex; gap:.3rem; align-items:center; background:var(--bg); border:1px solid var(--line); border-radius:999px; padding:.15rem .6rem; font-size:.8rem; }

.toast {
  position: fixed; left: 50%; bottom: 24px; transform: translateX(-50%);
  background: var(--ink); color: var(--bg); padding: .6rem 1rem; border-radius: 8px;
  box-shadow: var(--shadow); z-index: 60; max-width: 90vw;
}

.lock { text-align: center; padding: 2.5rem 1rem; }
.lock .big { font-size: 2rem; }

table.data { border-collapse: collapse; width: 100%; font-size: .9rem; }
table.data th, table.data td { border: 1px solid var(--line); padding: .35rem .55rem; text-align: left; }
table.data th { background: var(--bg); }

@media (max-width: 900px) {
  .runner { grid-template-columns: 1fr; }
  .runner .side { position: static; max-height: none; }
}