:root {
  --ink: #1F2328;
  --cost: #B4341A;
  --cache: #2D6A4F;
  --mute: #6E7781;
  --paper: #FFFFFF;
  --bg: #FAFAFA;
  --border: #E5E7EB;
  --code-bg: #F3F4F6;
  --max-w: 720px;
}

@media (prefers-color-scheme: dark) {
  :root {
    --ink: #E6EDF3;
    --cost: #E8695A;
    --cache: #5BB98B;
    --mute: #9CA3AF;
    --paper: #0D1117;
    --bg: #161B22;
    --border: #30363D;
    --code-bg: #1C2128;
  }
}

*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html {
  font-size: 17px;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
  color: var(--ink);
  background: var(--bg);
  line-height: 1.7;
  padding: 0;
}

/* --- Navigation --- */
.site-nav {
  background: var(--paper);
  border-bottom: 1px solid var(--border);
  padding: 0.75rem 1.5rem;
  position: sticky;
  top: 0;
  z-index: 100;
}
.site-nav-inner {
  max-width: var(--max-w);
  margin: 0 auto;
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
  flex-wrap: wrap;
}
.site-nav a {
  color: var(--mute);
  text-decoration: none;
  font-size: 0.85rem;
  transition: color 0.15s;
}
.site-nav a:hover { color: var(--ink); }
.site-nav .series-title {
  font-weight: 600;
  color: var(--ink);
  font-size: 0.9rem;
}
.nav-links { display: flex; gap: 1rem; flex-wrap: wrap; }

/* --- Article --- */
article {
  max-width: var(--max-w);
  margin: 0 auto;
  padding: 3rem 1.5rem 4rem;
}

article h1 {
  font-size: 2rem;
  line-height: 1.2;
  margin-bottom: 0.5rem;
  letter-spacing: -0.02em;
}

article .byline {
  color: var(--mute);
  font-size: 0.9rem;
  margin-bottom: 0.25rem;
}

article .series-note {
  color: var(--mute);
  font-size: 0.9rem;
  font-style: italic;
  margin-bottom: 2rem;
}

article hr {
  border: none;
  border-top: 1px solid var(--border);
  margin: 2rem 0;
}

article h2 {
  font-size: 1.45rem;
  margin: 2.5rem 0 0.75rem;
  letter-spacing: -0.01em;
}

article h3 {
  font-size: 1.15rem;
  margin: 2rem 0 0.6rem;
}

article p {
  margin-bottom: 1rem;
}

article a {
  color: var(--cache);
  text-decoration: underline;
  text-decoration-thickness: 1px;
  text-underline-offset: 2px;
}
article a:hover { text-decoration-thickness: 2px; }

article strong { font-weight: 600; }
article em { font-style: italic; }

article ul, article ol {
  margin: 0 0 1rem 1.5rem;
}
article li { margin-bottom: 0.35rem; }

article blockquote {
  border-left: 3px solid var(--cache);
  padding: 0.5rem 1rem;
  margin: 1rem 0;
  color: var(--mute);
}

/* --- Code --- */
article code {
  font-family: 'SF Mono', 'Fira Code', 'Cascadia Code', 'JetBrains Mono', monospace;
  font-size: 0.88em;
  background: var(--code-bg);
  padding: 0.15em 0.35em;
  border-radius: 3px;
}

article pre {
  background: var(--code-bg);
  padding: 1rem 1.25rem;
  border-radius: 6px;
  overflow-x: auto;
  margin: 1rem 0 1.5rem;
  border: 1px solid var(--border);
}
article pre code {
  background: none;
  padding: 0;
  font-size: 0.85rem;
  line-height: 1.5;
}

/* --- Figures / Visuals --- */
figure {
  margin: 2rem -1.5rem;
  background: var(--paper);
  border: 1px solid var(--border);
  border-radius: 8px;
  overflow: hidden;
}
figure iframe {
  display: block;
  width: 100%;
  border: 0;
}
figcaption {
  padding: 0.75rem 1.25rem;
  font-size: 0.85rem;
  color: var(--mute);
  border-top: 1px solid var(--border);
  line-height: 1.5;
}

/* --- Series nav (bottom) --- */
.series-nav {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin: 3rem 0 1rem;
  padding: 1.5rem 0;
  border-top: 1px solid var(--border);
}
.series-nav a {
  color: var(--cache);
  text-decoration: none;
  font-size: 0.9rem;
  font-weight: 500;
}
.series-nav a:hover { text-decoration: underline; }
.series-nav .prev::before { content: '\2190\00a0'; }
.series-nav .next::after { content: '\00a0\2192'; }

/* --- Footer --- */
.site-footer {
  max-width: var(--max-w);
  margin: 0 auto;
  padding: 2rem 1.5rem;
  border-top: 1px solid var(--border);
  color: var(--mute);
  font-size: 0.8rem;
  line-height: 1.6;
}
.site-footer a { color: var(--cache); }

/* --- Series index --- */
.series-index { list-style: none; margin: 2rem 0; padding: 0; }
.series-index li {
  border: 1px solid var(--border);
  border-radius: 8px;
  margin-bottom: 0.75rem;
  transition: border-color 0.15s;
}
.series-index li:hover { border-color: var(--cache); }
.series-index a {
  display: block;
  padding: 1.25rem 1.5rem;
  text-decoration: none;
  color: var(--ink);
}
.series-index .part-num {
  font-size: 0.8rem;
  color: var(--mute);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  display: block;
  margin-bottom: 0.2rem;
}
.series-index .part-title {
  font-size: 1.1rem;
  font-weight: 600;
  display: block;
  margin-bottom: 0.3rem;
}
.series-index .part-desc {
  font-size: 0.88rem;
  color: var(--mute);
  display: block;
}

/* --- Responsive --- */
@media (max-width: 600px) {
  html { font-size: 16px; }
  article { padding: 2rem 1rem 3rem; }
  article h1 { font-size: 1.6rem; }
  figure { margin: 1.5rem -1rem; }
  .series-nav { flex-direction: column; }
}