/* ============================================================
   Design tokens
   ============================================================ */
:root {
  --color-bg: #faf9f7;
  --color-bg-elevated: #ffffff;
  --color-text: #17181c;
  --color-text-muted: #63666f;
  --color-text-faint: #8b8e97;
  --color-border: #e6e3dd;
  --color-border-strong: #d6d2c8;
  --color-accent: #3548c8;
  --color-accent-ink: #ffffff;
  --color-accent-soft: #eceeff;
  --color-code-bg: #f1efe9;

  --part-0: 224 78% 46%;
  --part-1: 168 55% 34%;
  --part-2: 28 82% 47%;
  --part-3: 266 50% 52%;
  --part-4: 350 68% 47%;
  --part-5: 40 70% 40%;

  --font-serif: "Fraunces", "Iowan Old Style", "Palatino Linotype", Georgia, serif;
  --font-sans: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;

  --max-width: 1100px;
  --reading-width: 700px;
  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 20px;
  --shadow-sm: 0 1px 2px rgba(20, 20, 20, 0.05);
  --shadow-md: 0 10px 30px -12px rgba(20, 20, 20, 0.16);
  --shadow-lift: 0 18px 40px -16px rgba(20, 20, 20, 0.22);
}

:root[data-theme="dark"] {
  --color-bg: #0e0f13;
  --color-bg-elevated: #16181f;
  --color-text: #eceef3;
  --color-text-muted: #a2a6b3;
  --color-text-faint: #6d7180;
  --color-border: #262a35;
  --color-border-strong: #33384a;
  --color-accent: #8ea1ff;
  --color-accent-ink: #0e0f13;
  --color-accent-soft: #1b2036;
  --color-code-bg: #1b1d26;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.4);
  --shadow-md: 0 10px 30px -12px rgba(0, 0, 0, 0.55);
  --shadow-lift: 0 18px 40px -16px rgba(0, 0, 0, 0.65);
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --color-bg: #0e0f13;
    --color-bg-elevated: #16181f;
    --color-text: #eceef3;
    --color-text-muted: #a2a6b3;
    --color-text-faint: #6d7180;
    --color-border: #262a35;
    --color-border-strong: #33384a;
    --color-accent: #8ea1ff;
    --color-accent-ink: #0e0f13;
    --color-accent-soft: #1b2036;
    --color-code-bg: #1b1d26;
  }
}

/* ============================================================
   Reset & base
   ============================================================ */
* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body {
  margin: 0;
  background: var(--color-bg);
  color: var(--color-text);
  font-family: var(--font-sans);
  font-size: 17px;
  line-height: 1.6;
  transition: background 0.2s ease, color 0.2s ease;
}
img, svg { max-width: 100%; }
a { color: var(--color-accent); text-decoration: none; }
a:hover { text-decoration: underline; }
::selection { background: var(--color-accent-soft); }

.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 24px;
}

/* ============================================================
   Header
   ============================================================ */
.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background: color-mix(in srgb, var(--color-bg) 88%, transparent);
  backdrop-filter: saturate(140%) blur(10px);
  border-bottom: 1px solid var(--color-border);
}
.site-header .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding-top: 14px;
  padding-bottom: 14px;
}
.brand {
  display: flex;
  align-items: baseline;
  gap: 10px;
  color: var(--color-text);
  font-family: var(--font-serif);
  font-weight: 600;
  font-size: 1.05rem;
  white-space: nowrap;
}
.brand:hover { text-decoration: none; }
.brand .brand-kicker {
  font-family: var(--font-sans);
  font-weight: 600;
  font-size: 0.68rem;
  letter-spacing: 0.09em;
  text-transform: uppercase;
  color: var(--color-text-faint);
}
.header-actions {
  display: flex;
  align-items: center;
  gap: 14px;
}
.back-link {
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--color-text-muted);
}
.theme-toggle {
  appearance: none;
  border: 1px solid var(--color-border-strong);
  background: var(--color-bg-elevated);
  color: var(--color-text);
  width: 36px;
  height: 36px;
  border-radius: 999px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  font-size: 16px;
  line-height: 1;
  box-shadow: var(--shadow-sm);
  transition: transform 0.15s ease, box-shadow 0.15s ease;
}
.theme-toggle:hover { box-shadow: var(--shadow-md); transform: translateY(-1px); }
.theme-toggle:active { transform: translateY(0); }

/* ============================================================
   Reading progress bar (post pages)
   ============================================================ */
.progress-bar {
  position: fixed;
  top: 0;
  left: 0;
  height: 3px;
  width: 0%;
  background: var(--color-accent);
  z-index: 60;
  transition: width 0.08s linear;
}

/* ============================================================
   Hero (homepage)
   ============================================================ */
.hero {
  padding: 72px 0 48px;
  border-bottom: 1px solid var(--color-border);
}
.hero-kicker {
  font-size: 0.78rem;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--color-accent);
  margin: 0 0 14px;
}
.hero h1 {
  font-family: var(--font-serif);
  font-weight: 600;
  font-size: clamp(2.1rem, 5vw, 3.4rem);
  line-height: 1.08;
  margin: 0 0 20px;
  max-width: 14ch;
}
.hero p {
  font-size: 1.15rem;
  color: var(--color-text-muted);
  max-width: 620px;
  margin: 0 0 22px;
}
.hero-meta {
  display: flex;
  gap: 22px;
  flex-wrap: wrap;
  font-size: 0.92rem;
  color: var(--color-text-faint);
}
.hero-meta strong { color: var(--color-text); }

/* Part quick-jump nav */
.part-nav {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  padding: 22px 0 0;
}
.part-nav a {
  font-size: 0.82rem;
  font-weight: 600;
  padding: 7px 13px;
  border-radius: 999px;
  border: 1px solid var(--color-border-strong);
  color: var(--color-text-muted);
}
.part-nav a:hover {
  border-color: var(--color-accent);
  color: var(--color-accent);
  text-decoration: none;
}

/* ============================================================
   Part sections & card grid (homepage)
   ============================================================ */
.part-section { padding: 52px 0 8px; }
.part-heading {
  display: flex;
  align-items: baseline;
  gap: 14px;
  margin-bottom: 22px;
}
.part-heading .part-dot {
  width: 11px;
  height: 11px;
  border-radius: 50%;
  background: hsl(var(--part-hue));
  flex: none;
}
.part-heading h2 {
  font-family: var(--font-serif);
  font-size: 1.5rem;
  font-weight: 600;
  margin: 0;
}
.part-heading .part-count {
  color: var(--color-text-faint);
  font-size: 0.85rem;
}

.card-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 20px;
}
@media (max-width: 920px) { .card-grid { grid-template-columns: repeat(2, 1fr); } }
@media (max-width: 640px) { .card-grid { grid-template-columns: 1fr; } }

.card {
  --part-hue: 224 78% 46%;
  display: flex;
  flex-direction: column;
  background: var(--color-bg-elevated);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  overflow: hidden;
  box-shadow: var(--shadow-sm);
  transition: transform 0.18s ease, box-shadow 0.18s ease, border-color 0.18s ease;
}
.card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lift);
  border-color: var(--color-border-strong);
}
.card-swatch {
  height: 64px;
  background:
    radial-gradient(120% 140% at 0% 0%, hsl(var(--part-hue) / 0.55), transparent 60%),
    radial-gradient(120% 140% at 100% 100%, hsl(var(--part-hue) / 0.35), transparent 60%),
    hsl(var(--part-hue) / 0.14);
  position: relative;
}
.card-swatch::after {
  content: "";
  position: absolute;
  inset: 0;
  background-image: repeating-linear-gradient(135deg, hsl(var(--part-hue) / 0.16) 0 2px, transparent 2px 14px);
}
.card-body {
  padding: 18px 20px 20px;
  display: flex;
  flex-direction: column;
  gap: 10px;
  flex: 1;
}
.card-eyebrow {
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.07em;
  text-transform: uppercase;
  color: hsl(var(--part-hue));
}
.card h3 {
  font-family: var(--font-serif);
  font-size: 1.2rem;
  font-weight: 600;
  line-height: 1.3;
  margin: 0;
}
.card h3 a { color: var(--color-text); }
.card h3 a:hover { color: var(--color-accent); text-decoration: none; }
.card p.card-sub {
  font-size: 0.92rem;
  color: var(--color-text-muted);
  margin: 0;
  flex: 1;
}
.card-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  font-size: 0.78rem;
  color: var(--color-text-faint);
  margin-top: 4px;
}
.card-tags {
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
}

/* ============================================================
   Pills / tags
   ============================================================ */
.pill {
  display: inline-flex;
  align-items: center;
  font-size: 0.72rem;
  font-weight: 600;
  padding: 3px 9px;
  border-radius: 999px;
  background: var(--color-accent-soft);
  color: var(--color-accent);
  white-space: nowrap;
}

/* ============================================================
   Post page
   ============================================================ */
.post-shell {
  padding: 40px 0 96px;
}
.post-grid {
  display: grid;
  grid-template-columns: minmax(0, var(--reading-width)) 220px;
  gap: 56px;
  justify-content: center;
}
@media (max-width: 1080px) {
  .post-grid { grid-template-columns: minmax(0, var(--reading-width)); }
  .post-toc { display: none; }
}

.post-header { margin-bottom: 8px; }
.post-eyebrow {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 0.78rem;
  font-weight: 700;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: hsl(var(--part-hue));
  margin-bottom: 16px;
}
.post-header h1 {
  font-family: var(--font-serif);
  font-size: clamp(1.9rem, 4vw, 2.6rem);
  line-height: 1.15;
  font-weight: 600;
  margin: 0 0 14px;
}
.post-subtitle {
  font-size: 1.15rem;
  color: var(--color-text-muted);
  margin: 0 0 20px;
  line-height: 1.5;
}
.post-meta {
  display: flex;
  gap: 16px;
  flex-wrap: wrap;
  font-size: 0.86rem;
  color: var(--color-text-faint);
  padding-bottom: 26px;
  border-bottom: 1px solid var(--color-border);
  margin-bottom: 34px;
}

.post-body { font-size: 1.06rem; }
.post-body h2 {
  font-family: var(--font-serif);
  font-size: 1.5rem;
  font-weight: 600;
  margin: 2.1em 0 0.7em;
  scroll-margin-top: 90px;
}
.post-body h3 {
  font-family: var(--font-serif);
  font-size: 1.2rem;
  font-weight: 600;
  margin: 1.8em 0 0.6em;
  scroll-margin-top: 90px;
}
.post-body p { margin: 0 0 1.3em; }
.post-body ul, .post-body ol { margin: 0 0 1.3em; padding-left: 1.35em; }
.post-body li { margin-bottom: 0.5em; }
.post-body li > p { margin-bottom: 0.4em; }
.post-body strong { font-weight: 700; }
.post-body em { font-style: italic; }
.post-body a { text-decoration: underline; text-decoration-color: var(--color-border-strong); }
.post-body code {
  font-family: "SF Mono", "JetBrains Mono", Menlo, Consolas, monospace;
  font-size: 0.86em;
  background: var(--color-code-bg);
  padding: 0.15em 0.4em;
  border-radius: 5px;
}
.post-body pre {
  background: var(--color-code-bg);
  padding: 16px 18px;
  border-radius: var(--radius-sm);
  overflow-x: auto;
  margin: 0 0 1.4em;
}
.post-body pre code { background: none; padding: 0; }
.post-body blockquote {
  margin: 0 0 1.4em;
  padding: 4px 20px;
  border-left: 3px solid var(--color-accent);
  color: var(--color-text-muted);
  font-style: italic;
}
.post-body hr {
  border: none;
  border-top: 1px solid var(--color-border);
  margin: 2.6em 0;
}
.post-body table {
  width: 100%;
  border-collapse: collapse;
  margin: 0 0 1.6em;
  font-size: 0.94rem;
}
.post-body th, .post-body td {
  border: 1px solid var(--color-border);
  padding: 10px 12px;
  text-align: left;
  vertical-align: top;
}
.post-body th {
  background: var(--color-code-bg);
  font-weight: 700;
  font-size: 0.86rem;
}

/* Diagram figure */
.diagram-frame {
  margin: 2.2em 0;
  padding: 22px 22px 18px;
  background: var(--color-bg-elevated);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-sm);
}
.diagram-media { line-height: 0; }
.diagram-media svg { width: 100%; height: auto; display: block; }
.diagram-frame figcaption {
  font-size: 0.88rem;
  color: var(--color-text-muted);
  margin-top: 14px;
  line-height: 1.55;
}
.diagram-standalone-link {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: 0.8rem;
  font-weight: 600;
  margin-top: 12px;
}

/* Tags + hashtags at end of post */
.post-tags, .post-hashtags {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin: 2em 0;
}
.post-hashtags { font-size: 0.92rem; color: var(--color-accent); }

/* Table of contents */
.post-toc {
  position: sticky;
  top: 90px;
  align-self: start;
  font-size: 0.86rem;
}
.post-toc .toc-label {
  font-weight: 700;
  letter-spacing: 0.05em;
  text-transform: uppercase;
  font-size: 0.72rem;
  color: var(--color-text-faint);
  margin-bottom: 10px;
}
.post-toc ol {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: 9px;
  border-left: 1px solid var(--color-border);
}
.post-toc li { padding-left: 14px; }
.post-toc a { color: var(--color-text-muted); }
.post-toc a:hover { color: var(--color-accent); text-decoration: none; }

/* Prev/next nav */
.post-pager {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
  margin-top: 56px;
  padding-top: 32px;
  border-top: 1px solid var(--color-border);
}
@media (max-width: 560px) { .post-pager { grid-template-columns: 1fr; } }
.pager-link {
  display: flex;
  flex-direction: column;
  gap: 6px;
  padding: 16px 18px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  color: var(--color-text);
  transition: border-color 0.15s ease, transform 0.15s ease;
}
.pager-link:hover { border-color: var(--color-accent); transform: translateY(-2px); text-decoration: none; }
.pager-link.next { text-align: right; align-items: flex-end; }
.pager-direction {
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--color-text-faint);
}
.pager-title { font-family: var(--font-serif); font-size: 1rem; font-weight: 600; }

/* ============================================================
   Footer
   ============================================================ */
.site-footer {
  border-top: 1px solid var(--color-border);
  padding: 36px 0 60px;
  color: var(--color-text-faint);
  font-size: 0.85rem;
}
.site-footer .container {
  display: flex;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 10px;
}

/* ============================================================
   Misc utility
   ============================================================ */
.visually-hidden {
  position: absolute;
  width: 1px; height: 1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
  white-space: nowrap;
}