:root {
  --color-bg: #f5f7fa;
  --color-surface: #ffffff;
  --color-text: #1f2933;
  --color-text-muted: #52606d;
  --color-primary: #2563eb;
  --color-primary-dark: #1d4ed8;
  --color-border: #e4e7eb;
  --color-accent-bg: #eff6ff;
  --radius: 12px;
  --shadow: 0 1px 3px rgba(15, 23, 42, 0.08), 0 8px 24px rgba(15, 23, 42, 0.06);
  --max-width: 760px;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background: var(--color-bg);
  color: var(--color-text);
  font-family: "Hiragino Kaku Gothic ProN", "Hiragino Sans", "Yu Gothic",
    "Meiryo", system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  line-height: 1.85;
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

.page {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 20px 80px;
}

/* ---- Header ---- */
.site-header {
  text-align: center;
  padding: 56px 20px 40px;
}

.site-header .brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  font-size: 1.5rem;
  font-weight: 700;
  letter-spacing: 0.02em;
  color: var(--color-primary-dark);
}

.site-header .brand .dot {
  width: 12px;
  height: 12px;
  border-radius: 50%;
  background: var(--color-primary);
}

.site-header h1 {
  margin: 18px 0 6px;
  font-size: 2rem;
  font-weight: 700;
}

.site-header .meta {
  margin: 0;
  color: var(--color-text-muted);
  font-size: 0.9rem;
}

/* ---- Content card ---- */
.content {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 40px clamp(24px, 5vw, 56px);
}

.intro {
  margin-top: 0;
  color: var(--color-text-muted);
}

/* ---- Table of contents ---- */
.toc {
  background: var(--color-accent-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 20px 24px;
  margin: 28px 0 8px;
}

.toc h2 {
  margin: 0 0 12px;
  font-size: 1rem;
  color: var(--color-primary-dark);
}

.toc ol {
  margin: 0;
  padding-left: 1.4em;
  columns: 2;
  column-gap: 32px;
}

.toc li {
  margin-bottom: 6px;
}

.toc a {
  color: var(--color-text);
  text-decoration: none;
}

.toc a:hover {
  color: var(--color-primary);
  text-decoration: underline;
}

/* ---- Articles ---- */
article.section {
  padding-top: 28px;
  scroll-margin-top: 16px;
}

article.section h2 {
  font-size: 1.2rem;
  font-weight: 700;
  margin: 0 0 12px;
  padding-bottom: 8px;
  border-bottom: 2px solid var(--color-accent-bg);
}

article.section h2 .num {
  color: var(--color-primary);
  margin-right: 8px;
}

article.section p {
  margin: 0 0 12px;
}

article.section ol,
article.section ul {
  margin: 0 0 12px;
  padding-left: 1.5em;
}

article.section li {
  margin-bottom: 6px;
}

.note {
  background: var(--color-accent-bg);
  border-left: 4px solid var(--color-primary);
  border-radius: 0 8px 8px 0;
  padding: 14px 18px;
  margin: 16px 0;
  color: var(--color-text-muted);
  font-size: 0.95rem;
}

a {
  color: var(--color-primary);
}

/* ---- Footer ---- */
.site-footer {
  text-align: center;
  margin-top: 48px;
  color: var(--color-text-muted);
  font-size: 0.85rem;
}

.site-footer a {
  color: var(--color-text-muted);
}

/* ---- Responsive ---- */
@media (max-width: 600px) {
  body {
    font-size: 15px;
  }
  .toc ol {
    columns: 1;
  }
  .content {
    padding: 28px 20px;
  }
}