:root {
  --bg: #fbfbfc; --fg: #1b1c1e; --muted: #5f6368; --line: #dcdee1;
  --card: #ffffff; --accent: #1a5fb4; --warn: #9a3412; --ok: #166534;
  --code-bg: #f4f5f7;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #17181a; --fg: #e8e9ea; --muted: #9aa0a6; --line: #34363a;
    --card: #1f2023; --accent: #7cadf0; --warn: #f0a882; --ok: #86d6a4;
    --code-bg: #26282c;
  }
}
:root[data-theme="dark"] {
  --bg: #17181a; --fg: #e8e9ea; --muted: #9aa0a6; --line: #34363a;
  --card: #1f2023; --accent: #7cadf0; --warn: #f0a882; --ok: #86d6a4;
  --code-bg: #26282c;
}
* { box-sizing: border-box; }
body {
  margin: 0; background: var(--bg); color: var(--fg);
  font: 16px/1.6 system-ui, -apple-system, "Segoe UI", "Noto Sans SC", sans-serif;
}
.topbar {
  display: flex; align-items: center; gap: 12px; padding: 10px 16px;
  border-bottom: 1px solid var(--line); background: var(--card);
}
.brand { font-weight: 650; }
.who { margin-left: auto; color: var(--muted); font-size: 14px; }
.role { border: 1px solid var(--line); border-radius: 10px; padding: 0 6px; margin-left: 4px; }
.logout-form { margin: 0; }
main { padding: 16px; }
.lesson, .narrow { max-width: 860px; margin: 0 auto; }
.narrow { max-width: 380px; }
h1 { font-size: 24px; margin: 8px 0; }
h2 { font-size: 19px; margin: 0 0 8px; }
h3 { font-size: 15px; margin: 14px 0 6px; color: var(--muted); }
.card {
  background: var(--card); border: 1px solid var(--line); border-radius: 10px;
  padding: 14px 16px; margin: 14px 0;
}
.muted { color: var(--muted); font-size: 14px; }
.err, .warn { color: var(--warn); }
.notes { color: var(--muted); font-size: 14px; padding-left: 20px; }
.prewrap { white-space: pre-wrap; }
.statement { white-space: pre-wrap; }
.ask { color: var(--accent); font-size: 14px; margin: 2px 0; }
label.q { display: block; margin: 10px 0 4px; font-size: 14px; color: var(--muted); }
textarea, input[type=text], input[type=password], select {
  width: 100%; margin-top: 4px; padding: 8px; border: 1px solid var(--line);
  border-radius: 7px; background: var(--bg); color: var(--fg);
  font: inherit; font-size: 15px;
}
textarea.mono, pre, code, .mono {
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace; font-size: 14px;
}
textarea.code { min-height: 200px; tab-size: 4; }
pre {
  background: var(--code-bg); border: 1px solid var(--line); border-radius: 7px;
  padding: 8px; overflow: auto; white-space: pre-wrap; margin: 4px 0;
}
pre.mini { max-height: 110px; font-size: 13px; }
button {
  font: inherit; font-size: 15px; padding: 7px 14px; border-radius: 7px;
  border: 1px solid var(--line); background: var(--card); color: var(--fg);
  cursor: pointer;
}
button.primary { background: var(--accent); border-color: var(--accent); color: #fff; }
button:disabled { opacity: .5; cursor: default; }
button.linkish {
  border: 0; background: none; color: var(--accent); padding: 2px 4px;
  text-decoration: underline; cursor: pointer;
}
.row { display: flex; flex-wrap: wrap; gap: 8px; align-items: center; margin: 8px 0; }
.stack { display: flex; flex-direction: column; gap: 10px; }
.savebar {
  position: sticky; top: 0; z-index: 5; display: flex; gap: 12px; align-items: center;
  background: var(--card); border: 1px solid var(--line); border-radius: 8px;
  padding: 7px 12px; margin: 10px 0;
}
.state { font-size: 14px; font-weight: 600; }
.state.idle { color: var(--muted); }
.state.saving { color: var(--accent); }
.state.saved { color: var(--ok); }
.state.failed { color: var(--warn); }
.tag {
  font-size: 12px; font-weight: 400; color: var(--muted); border: 1px solid var(--line);
  border-radius: 10px; padding: 1px 7px; margin-left: 6px; vertical-align: middle;
}
.warn-tag { color: var(--warn); border-color: var(--warn); }
.samples { display: flex; flex-wrap: wrap; gap: 12px; }
.sample { flex: 1 1 220px; }
.sample .label, .label { font-size: 12px; color: var(--muted); margin-top: 4px; }
iframe#runnerFrame { width: 100%; height: 56px; border: 1px solid var(--line); border-radius: 7px; }
.grid { width: 100%; border-collapse: collapse; font-size: 14px; }
.grid th, .grid td { border-bottom: 1px solid var(--line); padding: 6px 8px; text-align: left; vertical-align: top; }
.grid.small { font-size: 13px; }
.cols { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; }
.attempt { border-left: 3px solid var(--line); padding-left: 10px; margin: 8px 0; }
.events { font-size: 14px; padding-left: 18px; }
.kv dt { font-weight: 600; font-size: 14px; margin-top: 6px; }
.kv dd { margin: 0 0 4px; font-size: 14px; }
.conflict { border: 1px solid var(--warn); border-radius: 8px; padding: 10px; margin-top: 10px; }
.teacher-only { margin-top: 12px; border: 1px dashed var(--warn); border-radius: 7px; padding: 8px; }
.teacher-only summary { cursor: pointer; color: var(--warn); font-size: 14px; }
.dim { display: inline-flex; flex-direction: column; font-size: 13px; color: var(--muted); width: 64px; }
.feedback p { margin: 6px 0; }
@media (max-width: 700px) {
  main { padding: 12px 16px; }
  .cols { grid-template-columns: 1fr; }
}

/* --- non-production environment banner ----------------------------------- */
/* Shown only when the environment is not production. Deliberately loud: the
   staging hostname is one word from production, and answers entered here do not
   count. Sticky so it stays visible while scrolling a long lesson page. */
.envbanner {
  position: sticky; top: 0; z-index: 20;
  background: #7c2d12; color: #fff;
  padding: 7px 16px; font-size: 14px; line-height: 1.45;
  border-bottom: 3px solid #fdba74;
  /* diagonal hazard stripes, kept subtle enough to read text over */
  background-image: repeating-linear-gradient(
    135deg, rgba(255,255,255,.08) 0 10px, rgba(255,255,255,0) 10px 20px);
}
.envbanner strong { letter-spacing: .04em; }
.envbanner-sub { display: block; font-size: 13px; opacity: .92; }
.envbanner code {
  background: rgba(255,255,255,.18); padding: 0 4px; border-radius: 4px;
}
/* The save-status bar is also sticky; offset it so the two do not overlap. */
.has-env-banner .savebar { top: 56px; }
@media (max-width: 700px) { .has-env-banner .savebar { top: 72px; } }
@media (prefers-reduced-motion: reduce) { .envbanner { background-image: none; } }