:root {
  --bg: #f4f5f7;
  --card: #ffffff;
  --text: #1d2129;
  --muted: #6b7280;
  --line: #e3e5e8;
  --accent: #1f5fbf;
  --accent-soft: #e8f0fc;
  --ok: #1a7f4b;
  --ok-soft: #e4f4ea;
  --warn: #b25b00;
  --warn-soft: #fdf0e1;
  --danger: #c0352b;
  --danger-soft: #fbe9e7;
  --radius: 10px;
  color-scheme: light;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #15171b;
    --card: #1e2126;
    --text: #e6e8eb;
    --muted: #9aa1ab;
    --line: #2e3238;
    --accent: #6ea2f0;
    --accent-soft: #1f2a3b;
    --ok: #5cc28b;
    --ok-soft: #1a2c22;
    --warn: #e6a457;
    --warn-soft: #33281b;
    --danger: #ef7a70;
    --danger-soft: #3a2120;
    color-scheme: dark;
  }
}

* { box-sizing: border-box; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font: 15px/1.6 -apple-system, "PingFang SC", "Microsoft YaHei", "Noto Sans SC", sans-serif;
}
.hidden { display: none !important; }
.wrap { max-width: 760px; margin: 0 auto; padding: 20px 16px 60px; }
.wrap.wide { max-width: 1400px; }

header.top {
  display: flex; align-items: center; justify-content: space-between; gap: 12px;
  flex-wrap: wrap; margin-bottom: 18px;
}
header.top h1 { font-size: 20px; margin: 0; }
header.top .sub { color: var(--muted); font-size: 13px; }

.card {
  background: var(--card); border: 1px solid var(--line); border-radius: var(--radius);
  padding: 18px; margin-bottom: 14px;
}
.auth { max-width: 400px; margin: 8vh auto 0; }
.auth h1 { font-size: 20px; text-align: center; margin: 0 0 4px; }
.auth .sub { text-align: center; color: var(--muted); font-size: 13px; margin-bottom: 18px; }

.tabs { display: flex; gap: 4px; border-bottom: 1px solid var(--line); margin-bottom: 16px; flex-wrap: wrap; }
.tabs button {
  background: none; border: 0; border-bottom: 2px solid transparent; padding: 8px 14px;
  font: inherit; color: var(--muted); cursor: pointer; margin-bottom: -1px;
}
.tabs button.active { color: var(--accent); border-color: var(--accent); font-weight: 600; }

label { display: block; font-size: 13px; color: var(--muted); margin: 10px 0 4px; }
input, select, textarea {
  width: 100%; font: inherit; color: var(--text); background: var(--card);
  border: 1px solid var(--line); border-radius: 8px; padding: 9px 11px;
}
input:focus, select:focus, textarea:focus { outline: 2px solid var(--accent-soft); border-color: var(--accent); }
textarea { resize: vertical; min-height: 120px; }

button.btn {
  font: inherit; border: 1px solid var(--line); background: var(--card); color: var(--text);
  border-radius: 8px; padding: 8px 14px; cursor: pointer; white-space: nowrap;
}
button.btn:hover { border-color: var(--accent); }
button.btn.primary { background: var(--accent); border-color: var(--accent); color: #fff; }
button.btn.danger { color: var(--danger); }
button.btn.small { padding: 4px 10px; font-size: 13px; }
button.btn:disabled { opacity: .5; cursor: default; }
.btn.block { width: 100%; margin-top: 16px; }

.msg { font-size: 13px; margin-top: 10px; min-height: 1em; }
.msg.err { color: var(--danger); }
.msg.ok { color: var(--ok); }

.pill { display: inline-block; font-size: 12px; padding: 1px 8px; border-radius: 99px; white-space: nowrap; }
.pill.open { background: var(--ok-soft); color: var(--ok); }
.pill.closed { background: var(--line); color: var(--muted); }
.pill.warn { background: var(--warn-soft); color: var(--warn); }

.stats { display: flex; gap: 10px; flex-wrap: wrap; margin-bottom: 14px; }
.stat { flex: 1 1 90px; background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); padding: 12px 14px; }
.stat b { display: block; font-size: 22px; font-variant-numeric: tabular-nums; }
.stat span { font-size: 12px; color: var(--muted); }

/* student assignment list */
.hw { display: grid; grid-template-columns: 1fr auto; gap: 6px 12px; align-items: center; padding: 14px 0; border-top: 1px solid var(--line); }
.hw:first-child { border-top: 0; padding-top: 0; }
.hw .title { font-weight: 600; }
.hw .meta { font-size: 12px; color: var(--muted); }
.hw .entry { display: flex; gap: 6px; align-items: center; }
.hw .entry input { width: 76px; text-align: center; padding: 7px 6px; font-variant-numeric: tabular-nums; }
.hw .score-ro { font-size: 20px; font-weight: 600; font-variant-numeric: tabular-nums; min-width: 40px; text-align: right; }
.hw details { grid-column: 1 / -1; }
.hw summary { cursor: pointer; color: var(--accent); font-size: 13px; }
.rubric { white-space: pre-wrap; word-break: break-word; background: var(--accent-soft); border-radius: 8px; padding: 10px 12px; margin-top: 6px; font-size: 14px; }

/* admin */
.toolbar { display: flex; gap: 8px; flex-wrap: wrap; align-items: center; margin-bottom: 12px; }
.toolbar input, .toolbar select { width: auto; min-width: 140px; }
.toolbar .grow { flex: 1; }
.table-wrap { overflow: auto; max-height: 72vh; border: 1px solid var(--line); border-radius: var(--radius); background: var(--card); }
table { border-collapse: collapse; width: 100%; font-size: 13px; }
th, td { border-bottom: 1px solid var(--line); padding: 6px 8px; text-align: left; white-space: nowrap; }
thead th { position: sticky; top: 0; background: var(--card); z-index: 2; font-weight: 600; box-shadow: 0 1px 0 var(--line); }
.grid td.sc, .grid th.sc { text-align: center; min-width: 52px; font-variant-numeric: tabular-nums; }
.grid th.sc { max-width: 90px; overflow: hidden; text-overflow: ellipsis; }
.grid td.sc { cursor: pointer; }
.grid td.sc:hover { background: var(--accent-soft); }
.grid td.sc.t { color: var(--warn); font-weight: 600; }
.grid td.sc input { width: 52px; padding: 2px 4px; text-align: center; }
.grid .sticky1, .grid .sticky2 { position: sticky; background: var(--card); z-index: 1; }
.grid .sticky1 { left: 0; }
.grid .sticky2 { left: 100px; box-shadow: 1px 0 0 var(--line); }
.grid thead .sticky1, .grid thead .sticky2 { z-index: 3; }
.grid td.sticky1, .grid th.sticky1 { min-width: 100px; max-width: 100px; }
.muted { color: var(--muted); }
.legend { font-size: 12px; color: var(--muted); margin-top: 8px; }
.legend .t { color: var(--warn); font-weight: 600; }

.asg-row input[type=text] { min-width: 160px; }
.rubric-preview { max-width: 360px; overflow: hidden; text-overflow: ellipsis; color: var(--muted); }
.switch { display: inline-flex; align-items: center; gap: 6px; cursor: pointer; margin: 0; color: var(--text); font-size: 13px; }
.switch input { width: auto; }

.two-col { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; }
@media (max-width: 760px) { .two-col { grid-template-columns: 1fr; } }
.form-row { display: flex; gap: 8px; flex-wrap: wrap; align-items: flex-end; }
.form-row > div { flex: 1 1 120px; }

dialog { border: 1px solid var(--line); border-radius: var(--radius); background: var(--card); color: var(--text); width: min(640px, calc(100vw - 32px)); padding: 18px; }
dialog::backdrop { background: rgba(0,0,0,.35); }
dialog h3 { margin: 0 0 8px; }
dialog textarea { min-height: 260px; }
.dlg-actions { display: flex; justify-content: flex-end; gap: 8px; margin-top: 12px; }

.toast { position: fixed; left: 50%; bottom: 24px; transform: translateX(-50%); background: var(--text); color: var(--bg); padding: 8px 16px; border-radius: 8px; font-size: 14px; z-index: 50; }