:root {
  color-scheme: light dark;
  --color-primary: #4f46e5;
  --color-primary-hover: #4338ca;
  --color-ink: #1e293b;
  --color-muted: #64748b;
  --color-background: #fafafc;
  --color-surface: #ffffff;
  --color-border: #e2e8f0;
  --color-soft-primary: #eef2ff;
  --color-soft-info: #eff6ff;
  --color-success: #047857;
  --color-warning: #c2410c;
  --color-danger: #dc2626;
  --color-focus: #3730a3;
  --shadow-card: 0 12px 32px rgb(30 41 59 / 8%);
  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-5: 1.25rem;
  --space-6: 1.5rem;
  --space-8: 2rem;
  --space-12: 3rem;
  --radius-control: 0.875rem;
  --radius-card: 1rem;
  --content-width: 70rem;
  --reading-width: 48rem;
  --font-sans: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", "Noto Sans JP", sans-serif;
}

@media (prefers-color-scheme: dark) {
  :root {
    --color-primary: #a5b4fc;
    --color-primary-hover: #c7d2fe;
    --color-ink: #f8fafc;
    --color-muted: #cbd5e1;
    --color-background: #0f172a;
    --color-surface: #1e293b;
    --color-border: #475569;
    --color-soft-primary: #312e81;
    --color-soft-info: #172554;
    --color-success: #6ee7b7;
    --color-warning: #fdba74;
    --color-danger: #fca5a5;
    --color-focus: #c7d2fe;
    --shadow-card: none;
  }
}

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

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background: var(--color-background);
  color: var(--color-ink);
  font-family: var(--font-sans);
  font-size: 1rem;
  line-height: 1.75;
  text-rendering: optimizeLegibility;
}

a {
  color: var(--color-primary);
  text-underline-offset: 0.2em;
  text-decoration-thickness: 0.08em;
}

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

a:focus-visible,
button:focus-visible {
  outline: 0.2rem solid var(--color-focus);
  outline-offset: 0.2rem;
}

img,
svg {
  display: block;
  max-width: 100%;
}

.skip-link {
  position: fixed;
  z-index: 100;
  top: var(--space-3);
  left: var(--space-3);
  padding: var(--space-3) var(--space-4);
  border-radius: var(--radius-control);
  background: var(--color-primary);
  color: var(--color-surface);
  transform: translateY(-160%);
}

.skip-link:focus {
  transform: translateY(0);
}

.site-header {
  border-bottom: 1px solid var(--color-border);
  background: color-mix(in srgb, var(--color-background) 92%, transparent);
}

.header-inner,
.site-footer,
.page-shell {
  width: min(calc(100% - 2rem), var(--content-width));
  margin-inline: auto;
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-4);
  min-height: 5rem;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: var(--space-3);
  color: var(--color-ink);
  font-weight: 750;
  text-decoration: none;
}

.brand img {
  width: 2.75rem;
  height: 2.75rem;
  border-radius: 0.75rem;
}

.site-nav ul {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
  margin: 0;
  padding: 0;
  list-style: none;
}

.site-nav a {
  display: inline-flex;
  align-items: center;
  min-height: 3rem;
  padding: var(--space-2) var(--space-3);
  border-radius: var(--radius-control);
  color: var(--color-muted);
  font-weight: 650;
  text-decoration: none;
}

.site-nav a:hover,
.site-nav a[aria-current="page"] {
  background: var(--color-soft-primary);
  color: var(--color-primary);
}

.page-shell {
  padding-block: var(--space-12);
}

.hero {
  display: grid;
  grid-template-columns: minmax(0, 1.3fr) minmax(15rem, 0.7fr);
  gap: var(--space-8);
  align-items: center;
  padding: clamp(1.5rem, 4vw, 3rem);
  border: 1px solid var(--color-border);
  border-radius: calc(var(--radius-card) + 0.25rem);
  background: linear-gradient(140deg, var(--color-surface), var(--color-soft-primary));
}

.hero-art {
  width: min(100%, 18rem);
  justify-self: center;
}

.eyebrow {
  margin: 0 0 var(--space-2);
  color: var(--color-primary);
  font-size: 0.875rem;
  font-weight: 750;
  letter-spacing: 0.06em;
}

h1,
h2,
h3 {
  margin-block: 0;
  line-height: 1.35;
  text-wrap: balance;
}

h1 {
  font-size: clamp(2rem, 7vw, 3.5rem);
}

h2 {
  font-size: clamp(1.5rem, 4vw, 2rem);
}

h3 {
  font-size: 1.125rem;
}

p,
ul,
ol {
  margin-block: var(--space-3) 0;
}

.lede {
  max-width: 40rem;
  color: var(--color-muted);
  font-size: 1.125rem;
}

.actions {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-3);
  margin-top: var(--space-6);
}

.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 3rem;
  padding: var(--space-3) var(--space-5);
  border: 1px solid var(--color-primary);
  border-radius: var(--radius-control);
  font-weight: 700;
  text-decoration: none;
}

.button-primary {
  background: var(--color-primary);
  color: var(--color-surface);
}

.button-primary:hover {
  background: var(--color-primary-hover);
  color: var(--color-surface);
}

.button-secondary {
  background: var(--color-surface);
  color: var(--color-primary);
}

.section {
  margin-top: var(--space-12);
}

.section-heading {
  max-width: var(--reading-width);
  margin-bottom: var(--space-6);
}

.grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: var(--space-5);
}

.card {
  padding: var(--space-6);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-card);
  background: var(--color-surface);
  box-shadow: var(--shadow-card);
}

.card p {
  color: var(--color-muted);
}

.card-link {
  display: inline-flex;
  align-items: center;
  min-height: 3rem;
  margin-top: var(--space-3);
  font-weight: 700;
}

.notice {
  max-width: var(--reading-width);
  padding: var(--space-5);
  border: 1px solid var(--color-border);
  border-left: 0.35rem solid var(--color-primary);
  border-radius: var(--radius-control);
  background: var(--color-soft-info);
}

.notice-warning {
  border-left-color: var(--color-warning);
}

.reading {
  max-width: var(--reading-width);
}

.reading > * + h2 {
  margin-top: var(--space-12);
}

.reading > * + h3 {
  margin-top: var(--space-8);
}

.reading li + li {
  margin-top: var(--space-2);
}

.steps {
  padding-left: 1.5rem;
}

.steps li {
  padding-left: var(--space-2);
}

.term-list {
  display: grid;
  grid-template-columns: minmax(10rem, 0.35fr) minmax(0, 1fr);
  gap: var(--space-3) var(--space-5);
  max-width: var(--reading-width);
  margin-top: var(--space-6);
}

.term-list dt {
  font-weight: 750;
}

.term-list dd {
  margin: 0;
  color: var(--color-muted);
}

.site-footer {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: var(--space-4);
  padding-block: var(--space-8);
  border-top: 1px solid var(--color-border);
  color: var(--color-muted);
  font-size: 0.875rem;
}

.site-footer ul {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-4);
  margin: 0;
  padding: 0;
  list-style: none;
}

@media (max-width: 48rem) {
  .header-inner {
    align-items: flex-start;
    flex-direction: column;
    padding-block: var(--space-4);
  }

  .hero,
  .grid {
    grid-template-columns: 1fr;
  }

  .hero-art {
    display: none;
  }

  .page-shell {
    padding-block: var(--space-8);
  }

  .term-list {
    grid-template-columns: 1fr;
  }

  .term-list dd + dt {
    margin-top: var(--space-3);
  }
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }
}