:root {
  --color-bg: #ffffff;
  --color-text: #1f2328;
  --color-muted: #57606a;
  --color-accent: #2f6f4f;
  --color-border: #e5e9ec;
  --color-surface: #f6f8f7;
  --max-width: 760px;
}

@media (prefers-color-scheme: dark) {
  :root {
    --color-bg: #14171a;
    --color-text: #e6e8ea;
    --color-muted: #a6adb4;
    --color-accent: #6fbf94;
    --color-border: #2a2e33;
    --color-surface: #1b1f23;
  }
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: "Hiragino Kaku Gothic ProN", "Hiragino Sans", "Yu Gothic UI", "Meiryo", sans-serif;
  background: var(--color-bg);
  color: var(--color-text);
  line-height: 1.8;
}

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

.site-header {
  border-bottom: 1px solid var(--color-border);
  padding: 40px 0 28px;
  text-align: center;
}

.site-header h1 {
  margin: 0 0 8px;
  font-size: 1.5rem;
  font-weight: 700;
}

.site-header .subtitle {
  margin: 0;
  color: var(--color-muted);
  font-size: 1rem;
}

main {
  padding: 40px 20px 60px;
}

.intro {
  color: var(--color-muted);
  margin-bottom: 32px;
}

.toc {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: 8px;
  padding: 20px 24px;
  margin-bottom: 40px;
}

.toc h2 {
  margin-top: 0;
  font-size: 1rem;
  color: var(--color-muted);
}

.toc ol {
  margin: 0;
  padding-left: 1.2em;
  columns: 2;
}

.toc a {
  color: var(--color-accent);
  text-decoration: none;
  font-size: 0.92rem;
}

.toc a:hover {
  text-decoration: underline;
}

section {
  margin-bottom: 36px;
  scroll-margin-top: 24px;
}

h2 {
  font-size: 1.15rem;
  border-left: 4px solid var(--color-accent);
  padding-left: 12px;
  margin-bottom: 14px;
}

h3 {
  font-size: 1rem;
  margin: 20px 0 8px;
}

ul {
  padding-left: 1.4em;
}

li {
  margin-bottom: 4px;
}

.contact {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: 8px;
  padding: 16px 20px;
}

.contact a {
  color: var(--color-accent);
}

.back-to-top {
  display: inline-block;
  color: var(--color-accent);
  text-decoration: none;
  font-size: 0.9rem;
  opacity: 0;
  visibility: hidden;
  transition: opacity 0.2s ease;
  position: fixed;
  bottom: 24px;
  right: 24px;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: 999px;
  padding: 8px 16px;
}

.back-to-top.visible {
  opacity: 1;
  visibility: visible;
}

.site-footer {
  border-top: 1px solid var(--color-border);
  padding: 20px 0;
  text-align: center;
  color: var(--color-muted);
  font-size: 0.85rem;
}