:root {
  --bg: #f5f7fa;
  --card: #ffffff;
  --text: #1c2430;
  --muted: #5d6b7c;
  --line: #d9e0e8;
  --brand: #0b5394;
  --brand-ink: #ffffff;
  --ok: #1e7b3c;
  --ok-bg: #e5f4ea;
  --warn: #8a5a00;
  --warn-bg: #fff4d6;
  --err: #b3261e;
  --err-bg: #fde8e6;
  --chip: #eef2f7;
  --answered: #0b5394;
  --radius: 10px;
  color-scheme: light;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #11161d;
    --card: #1a212b;
    --text: #e6ebf1;
    --muted: #9aa8b8;
    --line: #2c3746;
    --brand: #5aa2e6;
    --brand-ink: #0b1220;
    --ok: #7fd49a;
    --ok-bg: #173523;
    --warn: #f0c56a;
    --warn-bg: #3a2e12;
    --err: #ff9b93;
    --err-bg: #3e1c1a;
    --chip: #232c38;
    --answered: #5aa2e6;
    color-scheme: dark;
  }
}
* { box-sizing: border-box; }
[hidden] { display: none !important; }
html, body { margin: 0; }
body {
  background: var(--bg);
  color: var(--text);
  font: 16px/1.45 system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
}
a { color: var(--brand); }
h1 { font-size: 1.5rem; margin: 0 0 .75rem; }
h2 { font-size: 1.15rem; margin: 1.25rem 0 .5rem; }
.muted { color: var(--muted); }
.small { font-size: .875rem; }
.container { max-width: 1100px; margin: 0 auto; padding: 16px; }
.narrow { max-width: 520px; margin: 0 auto; }

.topbar {
  display: flex; flex-wrap: wrap; align-items: center; gap: 8px 16px;
  padding: 10px 16px; background: var(--card); border-bottom: 1px solid var(--line);
}
.topbar .brand { font-weight: 700; text-decoration: none; color: var(--text); }
.topbar nav { display: flex; flex-wrap: wrap; gap: 4px 14px; flex: 1; }
.topbar nav a { text-decoration: none; color: var(--muted); }
.topbar nav a.on { color: var(--brand); font-weight: 600; }
.topbar .who { font-size: .9rem; color: var(--muted); display: flex; gap: 8px; align-items: center; }

.card { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); padding: 16px; margin-bottom: 16px; }
.grid { display: grid; gap: 16px; grid-template-columns: repeat(auto-fit, minmax(280px, 1fr)); }
.row { display: flex; flex-wrap: wrap; gap: 8px; align-items: center; }
.spread { justify-content: space-between; }

.flash { padding: 10px 14px; border-radius: 8px; margin-bottom: 12px; }
.flash.ok { background: var(--ok-bg); color: var(--ok); }
.flash.error { background: var(--err-bg); color: var(--err); }
.flash.warn { background: var(--warn-bg); color: var(--warn); }

label { display: block; font-weight: 600; margin: 10px 0 4px; font-size: .95rem; }
label.inline { display: inline-flex; gap: 6px; align-items: center; font-weight: 400; margin: 0; }
input[type=text], input[type=password], input[type=number], input[type=date], input[type=url], select, textarea {
  width: 100%; padding: 10px 12px; font: inherit; color: var(--text);
  background: var(--card); border: 1px solid var(--line); border-radius: 8px;
}
textarea { min-height: 90px; }
input:focus, select:focus, textarea:focus { outline: 2px solid var(--brand); outline-offset: 1px; }
.hint { font-size: .85rem; color: var(--muted); margin-top: 4px; }

button, .btn {
  display: inline-flex; align-items: center; justify-content: center; gap: 6px;
  padding: 9px 16px; font: inherit; font-weight: 600; border-radius: 8px; cursor: pointer;
  border: 1px solid var(--brand); background: var(--brand); color: var(--brand-ink); text-decoration: none;
}
button.secondary, .btn.secondary { background: transparent; color: var(--brand); }
button.danger, .btn.danger { background: var(--err); border-color: var(--err); color: #fff; }
button.small, .btn.small { padding: 4px 10px; font-size: .85rem; }
button.link { background: none; border: 0; padding: 0; color: var(--brand); font-weight: 400; text-decoration: underline; }
button:disabled { opacity: .45; cursor: not-allowed; }
form.inline { display: inline; }

table { width: 100%; border-collapse: collapse; }
th, td { text-align: left; padding: 8px 10px; border-bottom: 1px solid var(--line); vertical-align: top; }
th { font-size: .85rem; color: var(--muted); font-weight: 600; }
.table-wrap { overflow-x: auto; }

.pill { display: inline-block; padding: 2px 9px; border-radius: 999px; font-size: .8rem; font-weight: 600; background: var(--chip); color: var(--muted); }
.pill.ok { background: var(--ok-bg); color: var(--ok); }
.pill.warn { background: var(--warn-bg); color: var(--warn); }
.pill.err { background: var(--err-bg); color: var(--err); }
.pill.info { background: var(--chip); color: var(--brand); }

.stats { display: flex; flex-wrap: wrap; gap: 12px; }
.stat { background: var(--chip); border-radius: 8px; padding: 8px 14px; min-width: 110px; }
.stat b { display: block; font-size: 1.4rem; }

/* ---------- student ---------- */
body.student .container { max-width: 680px; }
.student-brand { text-align: center; font-weight: 700; padding: 2px 0 6px; }
.student-brand a { color: var(--text); text-decoration: none; }
.student-head { text-align: center; padding: 18px 16px 4px; }
.student-head .t { font-weight: 700; }
.big-code { font-size: 1.6rem; letter-spacing: .2em; text-align: center; text-transform: uppercase; }
.suggest { position: relative; }
.suggest ul {
  position: absolute; z-index: 5; left: 0; right: 0; margin: 2px 0 0; padding: 0; list-style: none;
  background: var(--card); border: 1px solid var(--line); border-radius: 8px; box-shadow: 0 6px 20px rgba(0,0,0,.15);
}
.suggest li { padding: 10px 12px; cursor: pointer; }
.suggest li.on, .suggest li:hover { background: var(--chip); }
.picked { margin-top: 6px; font-size: .9rem; color: var(--ok); }

.exam-bar { display: flex; justify-content: space-between; align-items: center; gap: 8px; padding: 10px 0; font-size: .95rem; }
.timer { font-variant-numeric: tabular-nums; font-weight: 700; }
.timer.low { color: var(--err); }
.save-state { font-size: .85rem; }
.save-state.saving { color: var(--muted); }
.save-state.saved { color: var(--ok); }
.save-state.retry { color: var(--err); }
.qno { color: var(--muted); font-weight: 600; margin-bottom: 6px; }
.stem { font-size: 1.15rem; margin: 0 0 14px; white-space: pre-wrap; }
.choice {
  display: flex; gap: 12px; align-items: flex-start; width: 100%; text-align: left; margin: 0 0 10px;
  padding: 14px; background: var(--card); color: var(--text); border: 2px solid var(--line); border-radius: 10px; font-weight: 400;
}
.choice .k { flex: 0 0 auto; width: 30px; height: 30px; border-radius: 50%; display: grid; place-items: center; background: var(--chip); font-weight: 700; }
.choice.on { border-color: var(--answered); }
.choice.on .k { background: var(--answered); color: var(--brand-ink); }
.nav { display: flex; justify-content: space-between; gap: 10px; margin: 16px 0; }
.nav button { flex: 1; padding: 14px; font-size: 1.05rem; }
.palette { display: grid; grid-template-columns: repeat(auto-fill, minmax(40px, 1fr)); gap: 6px; margin: 10px 0 16px; }
.palette button { padding: 8px 0; background: var(--card); color: var(--text); border: 1px solid var(--line); font-weight: 600; }
.palette button.done { background: var(--answered); color: var(--brand-ink); border-color: var(--answered); }
.palette button.cur { outline: 3px solid var(--warn); outline-offset: 1px; }
.submit-row { text-align: center; margin: 18px 0 30px; }
.submit-row button { padding: 14px 40px; font-size: 1.1rem; }
.center { text-align: center; }
.spinner { width: 42px; height: 42px; border: 4px solid var(--line); border-top-color: var(--brand); border-radius: 50%; margin: 20px auto; animation: spin 1s linear infinite; }
@keyframes spin { to { transform: rotate(360deg); } }
.score-big { font-size: 3rem; font-weight: 800; color: var(--brand); }

/* ---------- lobby chat ---------- */
.chat-presence { border-bottom: 1px solid var(--line); padding-bottom: 12px; margin-bottom: 12px; }
.chat-people { display: flex; flex-wrap: wrap; gap: 6px; max-height: 120px; overflow-y: auto; margin-top: 8px; }
.chat-list {
  max-height: 300px; min-height: 80px; overflow-y: auto; display: flex; flex-direction: column; gap: 6px;
  padding: 8px; background: var(--bg); border: 1px solid var(--line); border-radius: 8px; text-align: left;
}
.chat-msg { padding: 6px 10px; border-radius: 8px; background: var(--card); border: 1px solid var(--line); word-wrap: break-word; white-space: pre-wrap; }
.chat-msg.mine { border-color: var(--answered); }
.chat-msg.instructor { background: var(--warn-bg); border-color: var(--warn); }
.chat-msg.hidden { opacity: .5; text-decoration: line-through; }
.chat-form { display: flex; gap: 8px; margin: 10px 0 6px; }
.chat-form input { flex: 1; }

/* ---------- presenter / results (projector) ---------- */
body.projector { background: var(--card); }
.present { display: grid; grid-template-columns: minmax(280px, 1fr) 1fr; gap: 32px; align-items: center; padding: 24px; min-height: 100vh; }
.present .qr svg { width: 100%; max-width: 520px; height: auto; background: #fff; padding: 12px; border-radius: 12px; }
.present h1 { font-size: 2.2rem; }
.present .code { font-size: 3.5rem; font-weight: 800; letter-spacing: .15em; color: var(--brand); }
.present .url { font-size: 1.3rem; word-break: break-all; }
.present .count { font-size: 2.5rem; font-weight: 800; }
.chips { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 12px; max-height: 40vh; overflow: auto; }
.chips span { background: var(--chip); padding: 4px 12px; border-radius: 999px; font-size: 1.05rem; }
.board td, .board th { font-size: 1.15rem; padding: 10px 14px; }
.bar { height: 14px; background: var(--brand); border-radius: 4px; }
.hist { display: flex; align-items: flex-end; gap: 6px; height: 160px; margin-top: 8px; }
.hist div { flex: 1; display: flex; flex-direction: column; justify-content: flex-end; align-items: center; font-size: .8rem; color: var(--muted); height: 100%; }
.hist i { display: block; width: 100%; background: var(--brand); border-radius: 4px 4px 0 0; }
.up { color: var(--ok); font-weight: 700; }
.down { color: var(--err); font-weight: 700; }
@media (max-width: 760px) {
  .present { grid-template-columns: 1fr; text-align: center; }
  .present .code { font-size: 2.4rem; }
}
@media print {
  .topbar, .no-print { display: none !important; }
  body { background: #fff; }
}