/* ----- Reset / base ----- */
*, *::before, *::after { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }
body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  font-size: 16px;
  line-height: 1.65;
  color: #1a1a1a;
  background: #fafaf7;
  -webkit-font-smoothing: antialiased;
}
a { color: #2b5fd9; text-decoration: none; }
a:hover { text-decoration: underline; }
h1, h2, h3, h4 { color: #111; line-height: 1.3; margin: 1.6em 0 0.6em; font-weight: 650; }
h1 { font-size: 2.1rem; margin-top: 0; }
h2 { font-size: 1.5rem; border-bottom: 1px solid #e5e2da; padding-bottom: 0.3em; }
h3 { font-size: 1.18rem; }
h4 { font-size: 1.0rem; color: #444; }
p { margin: 0.8em 0; }
ul, ol { padding-left: 1.4em; }
li { margin: 0.25em 0; }
hr { border: none; border-top: 1px solid #e5e2da; margin: 2em 0; }
small { color: #666; }
strong { font-weight: 650; color: #111; }

/* ----- Layout ----- */
.layout { display: grid; grid-template-columns: 280px 1fr; min-height: 100vh; }
.sidebar {
  background: #1d2230; color: #c9d1e0; padding: 1.5rem 1.1rem;
  border-right: 1px solid #11141d; position: sticky; top: 0; height: 100vh; overflow-y: auto;
}
.sidebar h2 { color: #fff; font-size: 1rem; text-transform: uppercase; letter-spacing: 0.05em; border: none; margin: 0 0 0.8em; }
.sidebar h2 a { color: #fff; }
.sidebar .sub { color: #7d869a; font-size: 0.8rem; margin: 0 0 1.2em; }
.sidebar ol { list-style: none; padding: 0; counter-reset: m; }
.sidebar li { counter-increment: m; margin: 0.15em 0; }
.sidebar li a {
  display: flex; align-items: center; gap: 0.5em;
  color: #c9d1e0; padding: 0.4em 0.55em; border-radius: 6px;
  font-size: 0.92rem; text-decoration: none;
}
.sidebar li a::before { content: counter(m, decimal-leading-zero); color: #5b6478; font-size: 0.78em; font-variant-numeric: tabular-nums; }
.sidebar li.glossary a::before { content: "§"; }
.sidebar li.home a::before { content: "▸"; }
.sidebar li a:hover { background: #2a3142; color: #fff; }
.sidebar li.current a { background: #2f7df0; color: #fff; }
.sidebar li.current a::before { color: #c5d8f8; }
.sidebar li.done a::after { content: "✓"; color: #6dd58c; margin-left: auto; font-weight: bold; }
.sidebar .lang-switch { margin-top: 1.5em; padding-top: 1em; border-top: 1px solid #2a3142; }
.sidebar .lang-switch label { font-size: 0.78rem; color: #7d869a; text-transform: uppercase; letter-spacing: 0.05em; display: block; margin-bottom: 0.4em; }
.sidebar .lang-switch .seg { display: inline-flex; background: #11141d; border-radius: 6px; padding: 2px; }
.sidebar .lang-switch button { background: none; border: none; color: #c9d1e0; padding: 0.3em 0.7em; cursor: pointer; border-radius: 4px; font-size: 0.85rem; }
.sidebar .lang-switch button.active { background: #2f7df0; color: #fff; }
.sidebar .progress-meta { margin-top: 1em; font-size: 0.78rem; color: #7d869a; }

.content { padding: 2.5rem 3rem 4rem; max-width: 880px; }
.content > header .lede { color: #555; font-size: 1.1rem; margin-top: 0.2em; }
.content > header .meta { color: #888; font-size: 0.85rem; }

/* ----- Callouts ----- */
.callout {
  border-left: 4px solid; padding: 0.9em 1.1em; margin: 1.4em 0; border-radius: 0 6px 6px 0;
}
.callout p:first-child { margin-top: 0; } .callout p:last-child { margin-bottom: 0; }
.callout .title { font-weight: 700; display: block; margin-bottom: 0.25em; font-size: 0.92rem; text-transform: uppercase; letter-spacing: 0.04em; }
.callout.tip       { background: #f0f7ff; border-color: #2f7df0; }
.callout.tip       .title { color: #1c4fb2; }
.callout.key       { background: #fff8e6; border-color: #e0a93b; }
.callout.key       .title { color: #8a6314; }
.callout.warn      { background: #fff1ed; border-color: #d8552b; }
.callout.warn      .title { color: #a13a14; }
.callout.pitfall   { background: #fdeef0; border-color: #c93055; }
.callout.pitfall   .title { color: #8a1a37; }
.callout.analogy   { background: #f1f4ea; border-color: #6f8c3a; }
.callout.analogy   .title { color: #4d6627; }
.callout.jarvis    { background: #eaf3f1; border-color: #2c8d7d; }
.callout.jarvis    .title { color: #1a5b50; }

/* ----- Code blocks with Python/TS tabs ----- */
.code {
  margin: 1.2em 0; border: 1px solid #e5e2da; border-radius: 8px; overflow: hidden; background: #1e2230;
}
.code .tabs { display: flex; background: #181b26; padding: 0 0.6em; }
.code .tabs button {
  background: none; border: none; color: #8d96ad; font-family: inherit; font-size: 0.82rem;
  padding: 0.55em 0.9em; cursor: pointer; border-bottom: 2px solid transparent;
}
.code .tabs button:hover { color: #fff; }
.code .tabs button.active { color: #fff; border-bottom-color: #2f7df0; }
.code .tabs .copy { margin-left: auto; color: #8d96ad; }
.code .tabs .copy:hover { color: #fff; }
.code pre {
  margin: 0; padding: 1em 1.2em; color: #e6e9f1; overflow-x: auto;
  font-family: "SF Mono", Menlo, Monaco, Consolas, "Liberation Mono", monospace;
  font-size: 0.88rem; line-height: 1.55;
}
.code pre[hidden] { display: none; }
.code pre code { background: none; padding: 0; color: inherit; }
/* Syntax highlighter colors */
.tok-kw  { color: #c792ea; }
.tok-str { color: #c3e88d; }
.tok-com { color: #6b7387; font-style: italic; }
.tok-num { color: #f78c6c; }
.tok-fn  { color: #82aaff; }
.tok-cls { color: #ffcb6b; }
.tok-op  { color: #89ddff; }
.tok-id  { color: #e6e9f1; }
.tok-dec { color: #f07178; }

/* Inline code */
:not(pre) > code {
  background: #efece4; color: #7a3a17; padding: 0.1em 0.4em; border-radius: 4px;
  font-family: "SF Mono", Menlo, Monaco, Consolas, monospace; font-size: 0.88em;
}

/* ----- Diagrams ----- */
.diagram {
  border: 1px solid #e5e2da; border-radius: 8px; padding: 1.3em; background: #fff;
  margin: 1.5em 0; overflow-x: auto;
}
.diagram .caption { color: #666; font-size: 0.85rem; margin-top: 0.6em; text-align: center; }
.boxes { display: flex; gap: 0.6em; align-items: stretch; flex-wrap: wrap; justify-content: center; }
.box {
  border: 1.5px solid #2f7df0; background: #eaf2ff; color: #1c4fb2;
  border-radius: 6px; padding: 0.6em 0.9em; font-size: 0.88rem; min-width: 110px; text-align: center;
  font-weight: 600;
}
.box.alt { border-color: #2c8d7d; background: #e6f3f0; color: #1a5b50; }
.box.muted { border-color: #999; background: #f3f1ec; color: #555; }
.box.tool { border-color: #e0a93b; background: #fff8e6; color: #8a6314; }
.arrow { display: flex; align-items: center; color: #888; font-size: 1.4em; }
.layer-cake { display: grid; gap: 0.5em; }
.layer {
  border: 1.5px solid #ccc; padding: 0.7em 1em; border-radius: 6px; font-weight: 600;
  background: #fff; display: flex; justify-content: space-between; align-items: center;
}
.layer .what { font-weight: 400; color: #666; font-size: 0.88rem; }
.layer.l1 { background: #fdeef0; border-color: #c93055; color: #8a1a37; }
.layer.l2 { background: #fff8e6; border-color: #e0a93b; color: #8a6314; }
.layer.l3 { background: #eaf3f1; border-color: #2c8d7d; color: #1a5b50; }
.layer.l4 { background: #eaf2ff; border-color: #2f7df0; color: #1c4fb2; }

/* ----- Quiz ----- */
.quiz {
  border: 1px solid #e5e2da; border-radius: 10px; padding: 1.3em 1.5em; margin: 2em 0; background: #fff;
}
.quiz h3 { margin-top: 0; font-size: 1.15rem; }
.quiz .q { margin: 1.2em 0; }
.quiz .q p.stem { font-weight: 600; margin-bottom: 0.5em; }
.quiz .opt {
  display: block; border: 1px solid #d6d2c5; border-radius: 6px; padding: 0.55em 0.9em;
  margin: 0.35em 0; cursor: pointer; background: #fafaf7;
}
.quiz .opt:hover { border-color: #2f7df0; }
.quiz .opt.correct { background: #e8f7ec; border-color: #6dd58c; color: #1a5b30; }
.quiz .opt.wrong   { background: #fce8eb; border-color: #c93055; color: #8a1a37; }
.quiz .opt input { margin-right: 0.6em; }
.quiz .feedback { margin-top: 0.6em; font-size: 0.92rem; color: #555; min-height: 1.2em; }
.quiz .feedback.show.correct { color: #1a5b30; }
.quiz .feedback.show.wrong   { color: #8a1a37; }

/* ----- Mark complete + prev/next ----- */
.mark-row { display: flex; justify-content: center; margin: 2em 0 1em; }
.btn {
  background: #2f7df0; color: #fff; border: none; padding: 0.7em 1.4em; font-size: 0.95rem;
  border-radius: 8px; cursor: pointer; font-weight: 600;
}
.btn:hover { background: #1c5fc8; }
.btn.done { background: #6dd58c; }
.btn.done::before { content: "✓ "; }

.prev-next { display: flex; justify-content: space-between; gap: 1em; margin-top: 2em; border-top: 1px solid #e5e2da; padding-top: 1.4em; }
.prev-next a {
  flex: 1; padding: 0.9em 1.1em; border: 1px solid #d6d2c5; border-radius: 8px; background: #fff;
  text-decoration: none; color: #1a1a1a; display: block;
}
.prev-next a:hover { border-color: #2f7df0; background: #f5f9ff; }
.prev-next .label { color: #888; font-size: 0.8rem; text-transform: uppercase; letter-spacing: 0.04em; display: block; }
.prev-next .title { font-weight: 600; }
.prev-next .next { text-align: right; }
.prev-next .next .label::after { content: " →"; }
.prev-next .prev .label::before { content: "← "; }
.prev-next .empty { visibility: hidden; }

/* ----- Index / landing ----- */
.hero {
  background: linear-gradient(135deg, #1d2230 0%, #2f4377 100%); color: #fff;
  padding: 3em 3em; border-radius: 14px; margin-bottom: 2em;
}
.hero h1 { color: #fff; margin: 0; font-size: 2.4rem; }
.hero p { color: #c9d1e0; font-size: 1.1rem; max-width: 60ch; }
.hero .tag { background: rgba(255,255,255,0.12); padding: 0.25em 0.75em; border-radius: 20px; font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.06em; display: inline-block; margin-bottom: 1em; }

.grid-modules { display: grid; grid-template-columns: repeat(auto-fill, minmax(260px, 1fr)); gap: 1em; margin: 1.5em 0; }
.card {
  border: 1px solid #e5e2da; border-radius: 10px; padding: 1.1em; background: #fff;
  text-decoration: none; color: inherit; display: block; transition: border-color 0.15s, transform 0.15s;
}
.card:hover { border-color: #2f7df0; transform: translateY(-2px); text-decoration: none; }
.card .n { color: #888; font-size: 0.8rem; font-variant-numeric: tabular-nums; }
.card h3 { margin: 0.3em 0; font-size: 1.05rem; }
.card p { margin: 0; color: #555; font-size: 0.9rem; }
.card .done-badge { display: none; color: #1a5b30; font-size: 0.78rem; font-weight: 600; }
.card.done .done-badge { display: inline; }

.toc { background: #fff; border: 1px solid #e5e2da; border-radius: 10px; padding: 1em 1.5em; margin: 1.2em 0; }
.toc ul { list-style: none; padding: 0; columns: 2; column-gap: 2em; }
.toc li { margin: 0.2em 0; break-inside: avoid; }

/* ----- Tables (used in some modules) ----- */
table { border-collapse: collapse; margin: 1.2em 0; width: 100%; }
th, td { border: 1px solid #e5e2da; padding: 0.55em 0.8em; text-align: left; font-size: 0.92rem; vertical-align: top; }
th { background: #f3f1ec; font-weight: 650; }

/* ----- Glossary ----- */
dl.glossary dt { font-weight: 700; color: #111; margin-top: 1em; }
dl.glossary dd { margin: 0.2em 0 0 0; color: #333; }
dl.glossary dd a { font-size: 0.85rem; color: #888; }

/* ----- Responsive ----- */
@media (max-width: 900px) {
  .layout { grid-template-columns: 1fr; }
  .sidebar { position: static; height: auto; }
  .content { padding: 1.5rem 1.2rem 3rem; }
  .hero { padding: 2em 1.5em; }
  .toc ul { columns: 1; }
}