:root {
  --bg: #f7f8fa;
  --panel: #ffffff;
  --text: #1f2430;
  --muted: #5c6470;
  --border: #dfe3ea;
  --source-accent: #7a6fb0;
  --source-soft: #eceef7;
  --ts: #2f74c0;
  --ts-soft: #e8f1fb;
  --pass: #1e7e46;
  --pass-soft: #e6f4ec;
  --fail: #b3382f;
  --fail-soft: #faeae8;
  --code-bg: #23262f;
  --code-text: #e6e9f0;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #14161c;
    --panel: #1d2027;
    --text: #e6e9f0;
    --muted: #9aa2af;
    --border: #32363f;
    --source-soft: #272b3a;
    --ts-soft: #1c2b3d;
    --pass: #4cc38a;
    --pass-soft: #17281f;
    --fail: #e5766c;
    --fail-soft: #33201e;
    --code-bg: #101218;
  }
}

* { box-sizing: border-box; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font: 16px/1.6 -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
}

#app, .page {
  max-width: 980px;
  margin: 0 auto;
  padding: 2rem 1.25rem 4rem;
}

a { color: var(--ts); }

h1 { font-size: 1.7rem; margin: 0.25rem 0 0.75rem; }
h2 { font-size: 1.15rem; margin: 0 0 0.6rem; }

.crumb { color: var(--muted); font-size: 0.85rem; margin: 0; }
.crumb a { color: var(--muted); }

.intro {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 1rem 1.25rem;
  margin-bottom: 1.25rem;
}

.intro table, .notes table, .cheatsheet table {
  border-collapse: collapse;
  width: 100%;
  margin: 0.75rem 0;
  font-size: 0.9rem;
}

.intro th, .intro td, .notes th, .notes td,
.cheatsheet th, .cheatsheet td {
  border: 1px solid var(--border);
  padding: 0.4rem 0.6rem;
  text-align: left;
  vertical-align: top;
}

.cheatsheet {
  margin-top: 3rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--border);
}
.cheat-intro { color: var(--muted); font-size: 0.9rem; margin: 0 0 1rem; }
.cheat-topic { margin: 1.5rem 0; }
.cheat-topic h3 { font-size: 1rem; margin: 0 0 0.4rem; }
.cheat-topic h3 a { color: inherit; text-decoration: none; }
.cheat-topic h3 a:hover { text-decoration: underline; }

.intro th, .notes th { background: var(--ts-soft); }

.intro code, .task-body code, .notes code {
  background: var(--source-soft);
  border-radius: 4px;
  padding: 0.1rem 0.35rem;
  font-family: "SF Mono", SFMono-Regular, Menlo, Consolas, monospace;
  font-size: 0.85em;
}

.compare {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1rem;
  margin-bottom: 1.25rem;
}

.panel {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 1rem 1.25rem;
  min-width: 0;
}

.source-panel { border-top: 3px solid var(--source-accent); }
.source-panel > summary {
  cursor: pointer;
  font-size: 1.15rem;
  font-weight: 600;
}
.source-panel[open] > summary { margin-bottom: 0.6rem; }
.task-panel { border-top: 3px solid var(--ts); }
.task-standalone { margin-bottom: 1.25rem; }
.task-ref {
  margin: 0.9rem 0 0;
  font-size: 0.9rem;
  color: var(--muted);
}

/* Source code and the editor stack full width, one above the other. */
.editor-panel {
  border-top: 3px solid var(--ts);
  display: flex;
  flex-direction: column;
}

.editor-panel #editor { flex: 1; }
.editor-panel .controls { margin-bottom: 0; }

.code-block {
  background: var(--code-bg);
  color: var(--code-text);
  border-radius: 8px;
  padding: 0.9rem 1rem;
  overflow-x: auto;
  font-size: 0.85rem;
  line-height: 1.55;
}

.code-block code {
  font-family: "SF Mono", SFMono-Regular, Menlo, Consolas, monospace;
}

.workspace {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 1rem 1.25rem;
  margin-bottom: 1.25rem;
}

#editor {
  width: 100%;
  min-height: 320px;
  resize: vertical;
  background: var(--code-bg);
  color: var(--code-text);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0.9rem 1rem;
  font-family: "SF Mono", SFMono-Regular, Menlo, Consolas, monospace;
  font-size: 0.9rem;
  line-height: 1.55;
  tab-size: 2;
}

#editor:focus { outline: 2px solid var(--ts); outline-offset: 1px; }

.controls {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin: 0.75rem 0;
  flex-wrap: wrap;
}

.btn {
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0.5rem 1.1rem;
  font-size: 0.95rem;
  cursor: pointer;
  background: var(--panel);
  color: var(--text);
}

.btn-run {
  background: var(--ts);
  border-color: var(--ts);
  color: #fff;
  font-weight: 600;
}

.btn-run:hover { filter: brightness(1.1); }
.btn-run:disabled { opacity: 0.6; cursor: wait; }
.btn-ghost:hover { border-color: var(--ts); }

.hint-key { color: var(--muted); font-size: 0.8rem; }

.run-status { color: var(--muted); font-style: italic; margin: 0.75rem 0 0; }

.test-results {
  list-style: none;
  padding: 0;
  margin: 0.75rem 0 0;
}

.test-results li {
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0.5rem 0.8rem;
  margin-bottom: 0.4rem;
  font-size: 0.92rem;
}

.test-results li.pass { background: var(--pass-soft); border-color: var(--pass); }
.test-results li.fail { background: var(--fail-soft); border-color: var(--fail); }

.test-results .mark { font-weight: 700; margin-right: 0.5rem; }
li.pass .mark { color: var(--pass); }
li.fail .mark { color: var(--fail); }

.test-results .detail {
  color: var(--muted);
  font-size: 0.83rem;
  margin: 0.2rem 0 0 1.4rem;
  font-family: "SF Mono", SFMono-Regular, Menlo, Consolas, monospace;
  white-space: pre-wrap;
}

.console-out {
  margin-top: 1rem;
}

.console-out h3 { font-size: 0.9rem; color: var(--muted); margin: 0 0 0.3rem; }

.console-out pre {
  background: var(--code-bg);
  color: var(--code-text);
  border-radius: 8px;
  padding: 0.7rem 0.9rem;
  font-size: 0.83rem;
  overflow-x: auto;
}

.success-banner {
  margin-top: 1rem;
  background: var(--pass-soft);
  border: 1px solid var(--pass);
  border-radius: 8px;
  padding: 0.75rem 1rem;
}

.solution { margin-top: 1.25rem; }
.results-area #results:empty + .solution { margin-top: 0; }
.solution summary { cursor: pointer; color: var(--muted); }
.solution .btn { margin-top: 0.5rem; }

.notes {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 1rem 1.25rem;
  margin-bottom: 1.25rem;
}

.lesson-nav {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  font-size: 0.95rem;
}

.site-footer {
  margin-top: 4rem;
  padding-top: 1.25rem;
  border-top: 1px solid var(--border);
  color: var(--muted);
  font-size: 0.85rem;
  text-align: center;
}
.site-footer a { color: inherit; }

/* index page */

.hero { margin-bottom: 1.5rem; }
.hero p { color: var(--muted); max-width: 46rem; }

.lesson-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.9rem;
  padding: 0;
  list-style: none;
}

@media (max-width: 800px) {
  .lesson-grid { grid-template-columns: 1fr; }
}

.lesson-card {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 0.9rem 1.1rem;
}

.lesson-card.done { border-color: var(--pass); }

.lesson-card a {
  font-weight: 600;
  text-decoration: none;
}

.lesson-card a:hover { text-decoration: underline; }

.lesson-card .blurb {
  color: var(--muted);
  font-size: 0.87rem;
  margin: 0.25rem 0 0;
}

.lesson-card .check { color: var(--pass); float: right; font-weight: 700; }