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

:root {
  --color-text: #37352f;
  --color-text-light: #787774;
  --color-bg: #ffffff;
  --color-border: #e9e9e7;
  --color-link: #37352f;
  --color-link-hover: #000000;
  --color-toggle-bg: #f7f6f3;
  --font: 'Rubik', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --max-width: 900px;
  --padding-x: 96px;
}

html, body {
  margin: 0;
  padding: 0;
  background: var(--color-bg);
  color: var(--color-text);
  font-family: var(--font);
  font-size: 16px;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

/* ---- Page layout ---- */
.page {
  max-width: calc(var(--max-width) + var(--padding-x) * 2);
  margin: 0 auto;
  padding: 0 var(--padding-x) 120px;
}

.page-header {
  padding-top: 60px;
  margin-bottom: 8px;
}

.page-title {
  font-size: 2.5rem;
  font-weight: 700;
  line-height: 1.2;
  margin: 0 0 8px;
  color: var(--color-text);
}

.content {
  margin-top: 16px;
}

/* ---- Divider ---- */
.divider {
  border: none;
  border-top: 1px solid var(--color-border);
  margin: 24px 0;
}

/* ---- Typography ---- */
h1 {
  font-size: 1.875rem;
  font-weight: 700;
  margin: 40px 0 8px;
  color: var(--color-text);
}

h1.section-title {
  font-size: 1.875rem;
  border-top: 1px solid var(--color-border);
  padding-top: 24px;
  margin-top: 48px;
}

h2 {
  font-size: 1.5rem;
  font-weight: 600;
  margin: 36px 0 8px;
  color: var(--color-text);
}

h3 {
  font-size: 1.25rem;
  font-weight: 600;
  margin: 24px 0 8px;
  color: var(--color-text);
}

p {
  margin: 8px 0;
}

.callout-italic {
  color: var(--color-text-light);
  margin: 16px 0;
}

.note {
  color: var(--color-text-light);
  font-size: 0.9375rem;
  margin: 4px 0 12px;
}

/* ---- Links ---- */
a {
  color: var(--color-link);
  text-decoration: underline;
  text-underline-offset: 2px;
}

a:hover {
  color: var(--color-link-hover);
}

/* ---- Lists ---- */
ul {
  margin: 4px 0 8px;
  padding-left: 24px;
}

ul li {
  margin: 4px 0;
  padding-left: 2px;
}

ul ul {
  margin: 4px 0;
}

/* ---- Table of contents ---- */
.toc {
  list-style: none;
  padding-left: 0;
  margin: 8px 0 24px;
  columns: 2;
  column-gap: 32px;
}

.toc li {
  padding-left: 0;
  margin: 3px 0;
  break-inside: avoid;
}

.toc a {
  font-size: 0.9375rem;
}

/* ---- Toggle (details/summary) ---- */
details.toggle {
  margin: 6px 0 4px;
}

details.toggle > summary {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  cursor: pointer;
  list-style: none;
  font-size: 0.9375rem;
  color: var(--color-text-light);
  padding: 2px 4px;
  border-radius: 4px;
  user-select: none;
  transition: background 150ms ease;
}

details.toggle > summary::-webkit-details-marker {
  display: none;
}

details.toggle > summary::before {
  content: "▶";
  font-size: 0.6rem;
  display: inline-block;
  transition: transform 150ms ease;
  color: var(--color-text-light);
  flex-shrink: 0;
}

details.toggle[open] > summary::before {
  transform: rotate(90deg);
}

details.toggle > summary:hover {
  background: var(--color-toggle-bg);
}

details.toggle > summary strong {
  font-weight: 500;
}

.toggle-body {
  margin: 6px 0 4px 20px;
  padding: 8px 12px;
  background: var(--color-toggle-bg);
  border-radius: 4px;
  font-size: 0.9375rem;
  color: var(--color-text);
  line-height: 1.6;
}

.toggle-body p {
  margin: 6px 0;
}

.toggle-body ul {
  margin: 6px 0;
}

/* ---- Mobile ---- */
@media (max-width: 768px) {
  :root {
    --padding-x: 24px;
  }

  .navbar {
    padding: 0 24px;
  }

  .page-title {
    font-size: 1.875rem;
  }

  h1 {
    font-size: 1.5rem;
  }

  h2 {
    font-size: 1.25rem;
  }

  .toc {
    columns: 1;
  }
}