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

/* ── Custom properties ─────────────────────────── */
:root {
  /* Light mode */
  --bg:        #fafaf9;
  --bg-alt:    #f5f5f4;
  --text:      #1c1917;
  --text-dim:  #57534e;
  --accent:    #b45309;       /* warm amber */
  --accent-h:  #92400e;
  --border:    #e7e5e4;
  --table-head:#f5f5f4;
  --table-row:#fafaf9;
  --code-bg:   #f5f5f4;
  --shadow:    rgba(0,0,0,.06);

  --serif:    Georgia, "Times New Roman", "Noto Serif", serif;
  --sans:     -apple-system, "Segoe UI", "Helvetica Neue", Arial, sans-serif;
  --mono:     "JetBrains Mono", "Fira Code", "Cascadia Code", ui-monospace, monospace;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg:       #18181b;
    --bg-alt:   #27272a;
    --text:     #f5f5f4;
    --text-dim: #a1a1aa;
    --accent:   #f59e0b;
    --accent-h: #d97706;
    --border:   #3f3f46;
    --table-head:#27272a;
    --table-row:#18181b;
    --code-bg:  #27272a;
    --shadow:   rgba(0,0,0,.3);
  }
}

[data-theme="dark"] {
  --bg:       #18181b;
  --bg-alt:   #27272a;
  --text:     #f5f5f4;
  --text-dim: #a1a1aa;
  --accent:   #f59e0b;
  --accent-h: #d97706;
  --border:   #3f3f46;
  --table-head:#27272a;
  --table-row:#18181b;
  --code-bg:  #27272a;
  --shadow:   rgba(0,0,0,.3);
}

/* ── Typography ────────────────────────────────── */
html { font-size: 17px; }

body {
  font-family: var(--serif);
  color: var(--text);
  background: var(--bg);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

h1, h2, h3, h4 {
  font-family: var(--sans);
  font-weight: 600;
  letter-spacing: -0.02em;
  line-height: 1.25;
  margin: 2em 0 .6em;
}

h1 { font-size: 2.4rem; }
h2 { font-size: 1.6rem; }
h3 { font-size: 1.2rem; }

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

p + p { margin-top: 1.2em; }

/* ── Layout ────────────────────────────────────── */
.page {
  max-width: 72ch;
  margin: 0 auto;
  padding: 2rem 1.5rem;
}

header.site-header {
  border-bottom: 1px solid var(--border);
  padding: 1rem 1.5rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  position: sticky;
  top: 0;
  background: var(--bg);
  z-index: 10;
}

header.site-header h1 {
  margin: 0;
  font-size: 1.1rem;
}

header.site-header h1 a { color: var(--text); }

nav.nav a {
  margin-left: 1.5rem;
  font-family: var(--sans);
  font-size: .85rem;
  color: var(--text-dim);
  transition: color .15s;
}
nav.nav a:hover { color: var(--accent); text-decoration: none; }

/* ── Hero (index) ─────────────────────────────── */
.hero {
  text-align: center;
  padding: 4rem 0 3rem;
}

.hero h1 { font-size: 3rem; margin-bottom: .5rem; }
.hero .subtitle {
  font-family: var(--sans);
  color: var(--text-dim);
  font-size: 1.1rem;
  max-width: 40ch;
  margin: 0 auto;
}

/* ── Book cards ────────────────────────────────── */
.books {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 1.2rem;
  margin: 2.5rem 0;
}

.book-card {
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 1.4rem;
  background: var(--bg-alt);
  transition: box-shadow .2s;
}
.book-card:hover { box-shadow: 0 2px 12px var(--shadow); }

.book-card h3 {
  font-size: 1rem;
  margin: 0 0 .4rem;
}

.book-card .author {
  font-family: var(--sans);
  font-size: .85rem;
  color: var(--text-dim);
  margin-bottom: .6rem;
}

.book-card .year {
  font-family: var(--sans);
  font-size: .75rem;
  color: var(--accent);
  font-weight: 600;
}

/* ── Chapter list ──────────────────────────────── */
.part-label {
  font-family: var(--sans);
  font-size: .8rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: .08em;
  color: var(--text-dim);
  margin: 2.5rem 0 .8rem;
  border-top: 1px solid var(--border);
  padding-top: 1rem;
}

.chapter-list { list-style: none; }
.chapter-list li {
  padding: .3rem 0;
}
.chapter-list a {
  font-size: 1rem;
}
.chapter-list .part-label + .chapter-list a {
  margin-top: .4rem;
}

/* ── Chapter page ──────────────────────────────── */
.chapter-meta {
  font-family: var(--sans);
  font-size: .8rem;
  color: var(--text-dim);
  margin-bottom: 1rem;
}

.chapter-body h2 {
  font-size: 1.35rem;
  margin-top: 2.5rem;
}

/* Entry-points table */
.entry-table {
  width: 100%;
  border-collapse: collapse;
  margin: 1.5rem 0 2rem;
  font-size: .9rem;
}

.entry-table th {
  text-align: left;
  font-family: var(--sans);
  font-weight: 600;
  font-size: .8rem;
  text-transform: uppercase;
  letter-spacing: .05em;
  color: var(--text-dim);
  padding: .7rem .8rem;
  background: var(--table-head);
  border-bottom: 2px solid var(--border);
}

.entry-table td {
  padding: .7rem .8rem;
  border-bottom: 1px solid var(--border);
  vertical-align: top;
}

.entry-table tr:nth-child(even) td {
  background: var(--table-row);
}

.entry-table .author-cell {
  font-family: var(--sans);
  font-weight: 600;
  white-space: nowrap;
  width: 140px;
}

/* ── Read-the-originals box ────────────────────── */
.read-originals {
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 1.2rem 1.4rem;
  margin: 2rem 0;
  background: var(--bg-alt);
}

.read-originals h3 {
  font-family: var(--sans);
  font-size: .9rem;
  text-transform: uppercase;
  letter-spacing: .05em;
  color: var(--text-dim);
  margin: 0 0 .8rem;
}

.read-originals ul {
  list-style: none;
  padding: 0;
}
.read-originals li {
  padding: .3rem 0;
  font-size: .9rem;
}
.read-originals li::before {
  content: "→ ";
  color: var(--accent);
}

/* ── Nav (prev / next) ────────────────────────── */
.chapter-nav {
  display: flex;
  justify-content: space-between;
  padding: 2rem 0;
  border-top: 1px solid var(--border);
  margin-top: 3rem;
}

.chapter-nav a {
  font-family: var(--sans);
  font-size: .85rem;
  color: var(--text-dim);
}
.chapter-nav a:hover { color: var(--accent); }
.chapter-nav a.next { text-align: right; }

/* ── Theme toggle ──────────────────────────────── */
.theme-toggle {
  background: none;
  border: 1px solid var(--border);
  border-radius: 4px;
  padding: .3rem .6rem;
  cursor: pointer;
  font-size: .8rem;
  color: var(--text-dim);
  transition: color .15s, border-color .15s;
}
.theme-toggle:hover {
  color: var(--accent);
  border-color: var(--accent);
}

/* ── Footer ────────────────────────────────────── */
footer {
  text-align: center;
  font-family: var(--sans);
  font-size: .75rem;
  color: var(--text-dim);
  padding: 2rem 0;
  border-top: 1px solid var(--border);
  margin-top: 2rem;
}

/* ── Upcoming (unwritten) chapter ──────────────── */
.chapter-list li.upcoming {
  color: var(--text-dim);
}
.chapter-list li.upcoming .upcoming-tag {
  font-family: var(--sans);
  font-size: .7rem;
  text-transform: uppercase;
  letter-spacing: .06em;
  color: var(--text-dim);
  border: 1px solid var(--border);
  border-radius: 3px;
  padding: .05em .4em;
  margin-left: .5rem;
  vertical-align: middle;
}

/* ── Unverified reference marker ───────────────── */
.unverified {
  font-style: italic;
  font-size: .8em;
  color: var(--accent);
  border-bottom: 1px dotted var(--accent);
  cursor: help;
}

/* ── KaTeX ─────────────────────────────────────── */
.katex-display {
  margin: 1.5rem 0;
  overflow-x: auto;
  overflow-y: hidden;
}

/* ── Print ─────────────────────────────────────── */
@media print {
  header.site-header, .chapter-nav, footer, .theme-toggle { display: none; }
  .page { max-width: 100%; padding: 0; }
  body { color: #000; background: #fff; }
  a { color: #000; }
  a[href]::after { content: " (" attr(href) ")"; font-size: .75rem; }
}

/* ── Essay template (rework) ───────────────────── */
.lede {
  font-size: 1.12rem;
  color: var(--text);
  margin-bottom: 1.2em;
}

.essay ul, .essay ol { padding-left: 1.3em; margin: 1.2em 0; }
.essay li + li { margin-top: .6em; }
.essay h2 + p, .essay .katex-display + p, .essay ul + p, .essay ol + p,
.essay details + p, .essay figure + p, .essay aside + p { margin-top: 1.2em; }

/* Reminders: short and skippable */
.reminders {
  border-left: 3px solid var(--accent);
  background: var(--bg-alt);
  padding: 1rem 1.3rem;
  margin: 2rem 0;
  font-size: .93rem;
  line-height: 1.6;
}
.reminders h2 {
  font-size: .8rem;
  text-transform: uppercase;
  letter-spacing: .06em;
  color: var(--text-dim);
  margin: 0 0 .6rem;
}
.reminders ul { margin: 0; }

/* Worked example: set off by a rule, not a box */
.worked {
  border-left: 1px solid var(--border);
  padding-left: 1.3rem;
}

/* Optional branches and worked answers */
details {
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: .8rem 1.1rem;
  margin: 1.5rem 0;
  background: var(--bg-alt);
  font-size: .95rem;
}
summary {
  font-family: var(--sans);
  font-size: .9rem;
  color: var(--accent);
  cursor: pointer;
}
details[open] summary { margin-bottom: .8rem; }
.questions p + details { margin-top: .8rem; }

/* Figures */
figure { margin: 2rem 0; }
figcaption {
  font-family: var(--sans);
  font-size: .82rem;
  line-height: 1.55;
  color: var(--text-dim);
  margin-top: .6rem;
}
.fig-svg { width: 100%; height: auto; display: block; }
.fig-axis { stroke: var(--text-dim); stroke-width: 1; fill: none; }
.fig-tick, .fig-label, .fig-note { font-family: var(--sans); fill: var(--text-dim); }
.fig-tick { font-size: 12px; }
.fig-label { font-size: 13px; }
.fig-note { font-size: 12.5px; fill: var(--text); }
.fig-band { fill: var(--accent); opacity: .1; }
.fig-dot, .fig-arrowhead { fill: var(--accent); }
.fig-arrowhead-mid { fill: var(--text); }
.fig-curve { fill: none; stroke-width: 2; stroke-linejoin: round; }
.fig-hot { stroke: var(--accent); stroke-width: 2.4; }
.fig-mid { stroke: var(--text); }
.fig-cool { stroke: var(--text-dim); }
.fig-classical { stroke: var(--text-dim); stroke-dasharray: 6 5; stroke-width: 1.6; }

@media print {
  details { break-inside: avoid; border: none; padding: 0; }
  details > * { display: block !important; }
  figure, .worked { break-inside: avoid; }
}

@media (max-width: 480px) {
  .worked { padding-left: .8rem; }
  .katex-display { font-size: .9em; }
}

/* Figures on phones: keep labels at their designed size and let the figure scroll */
@media (max-width: 600px) {
  .fig-scroll { overflow-x: auto; -webkit-overflow-scrolling: touch; }
  .fig-scroll .fig-svg { min-width: 640px; }
  figure:has(.fig-scroll) figcaption::before {
    content: "Scroll sideways to see the whole figure. ";
    font-style: italic;
  }
}

@media print {
  details::details-content { content-visibility: visible; }
  summary { color: #000; }
  .fig-scroll { overflow: visible; }
  .fig-scroll .fig-svg { min-width: 0; }
  figure figcaption::before { content: none !important; }
}

/* Small notation tables inside essays */
.notation-table {
  width: 100%;
  border-collapse: collapse;
  margin: 1.5rem 0;
  font-size: .9rem;
  display: block;
  overflow-x: auto;
}
.notation-table th {
  text-align: left;
  font-family: var(--sans);
  font-size: .78rem;
  text-transform: uppercase;
  letter-spacing: .05em;
  color: var(--text-dim);
  padding: .5rem .7rem;
  border-bottom: 2px solid var(--border);
}
.notation-table td {
  padding: .5rem .7rem;
  border-bottom: 1px solid var(--border);
  vertical-align: top;
}

/* Homepage map: essay title with its question */
.chapter-list.map { list-style: decimal; padding-left: 1.6em; }
.chapter-list.map li { padding: .45rem 0; }
.map-q {
  display: block;
  font-size: .9rem;
  color: var(--text-dim);
  line-height: 1.45;
}
.map-note {
  font-family: var(--sans);
  font-size: .85rem;
  color: var(--text-dim);
}