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

:root {
  --ink: #172033;
  --muted: #5f6b7a;
  --line: #dfe5ee;
  --paper: #ffffff;
  --soft: #f6f8fb;
  --blue: #2563eb;
  --blue-dark: #1d4ed8;
  --green: #047857;
  --amber: #b45309;
  --shadow: 0 20px 50px rgba(23, 32, 51, 0.08);
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Noto Sans JP", "Hiragino Sans", "Yu Gothic", sans-serif;
  color: var(--ink);
  background: var(--paper);
  line-height: 1.8;
}

a {
  color: var(--blue-dark);
  text-decoration-thickness: 0.08em;
  text-underline-offset: 0.18em;
}

.seo-nav {
  border-bottom: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.94);
  position: sticky;
  top: 0;
  z-index: 10;
  backdrop-filter: blur(10px);
}

.seo-nav__inner,
.seo-container {
  width: min(1120px, calc(100% - 40px));
  margin: 0 auto;
}

.seo-nav__inner {
  min-height: 64px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
}

.seo-logo {
  color: var(--ink);
  font-weight: 800;
  text-decoration: none;
}

.seo-nav__links {
  display: flex;
  align-items: center;
  gap: 18px;
  font-size: 14px;
}

.seo-hero {
  background: linear-gradient(180deg, #eef5ff 0%, #ffffff 100%);
  border-bottom: 1px solid var(--line);
}

.seo-hero__grid {
  display: grid;
  grid-template-columns: minmax(0, 1.15fr) minmax(320px, 0.85fr);
  gap: 48px;
  align-items: center;
  padding: 72px 0;
}

.seo-eyebrow {
  color: var(--blue-dark);
  font-size: 13px;
  font-weight: 800;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.seo-hero h1,
.seo-article h1 {
  margin: 14px 0 18px;
  font-size: clamp(34px, 5vw, 56px);
  line-height: 1.16;
  letter-spacing: 0;
}

.seo-lead {
  color: var(--muted);
  font-size: 18px;
  max-width: 760px;
}

.seo-actions {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
  margin-top: 28px;
}

.seo-button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 48px;
  padding: 0 20px;
  border-radius: 8px;
  border: 1px solid var(--line);
  background: var(--paper);
  color: var(--ink);
  font-weight: 700;
  text-decoration: none;
}

.seo-button--primary {
  background: var(--blue);
  border-color: var(--blue);
  color: #ffffff;
}

.seo-visual {
  border-radius: 12px;
  overflow: hidden;
  box-shadow: var(--shadow);
  border: 1px solid var(--line);
  background: var(--soft);
}

.seo-visual img {
  display: block;
  width: 100%;
  height: auto;
}

.seo-section {
  padding: 64px 0;
  border-bottom: 1px solid var(--line);
}

.seo-section h2 {
  margin: 0 0 18px;
  font-size: clamp(26px, 3vw, 36px);
  line-height: 1.25;
}

.seo-section h3 {
  margin: 0 0 8px;
  font-size: 19px;
}

.seo-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 18px;
  margin-top: 28px;
}

.seo-grid--two {
  grid-template-columns: repeat(2, 1fr);
}

.seo-card {
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 22px;
  background: var(--paper);
}

.seo-card p {
  margin: 0;
  color: var(--muted);
}

.seo-note {
  padding: 18px 20px;
  border-radius: 10px;
  background: #fff7ed;
  border: 1px solid #fed7aa;
  color: #7c2d12;
}

.seo-table-wrap {
  overflow-x: auto;
  margin-top: 24px;
}

.seo-table {
  width: 100%;
  min-width: 720px;
  border-collapse: collapse;
  border: 1px solid var(--line);
}

.seo-table th,
.seo-table td {
  border-bottom: 1px solid var(--line);
  padding: 14px 16px;
  text-align: left;
  vertical-align: top;
}

.seo-table th {
  background: var(--soft);
}

.seo-article {
  width: min(840px, calc(100% - 40px));
  margin: 0 auto;
  padding: 56px 0 72px;
}

.seo-article h2 {
  margin-top: 44px;
  font-size: 28px;
  line-height: 1.3;
}

.seo-article p,
.seo-article li {
  color: #344054;
}

.seo-article ul,
.seo-article ol {
  padding-left: 1.4em;
}

.seo-related {
  margin-top: 48px;
  padding: 24px;
  border: 1px solid var(--line);
  border-radius: 10px;
  background: var(--soft);
}

.seo-footer {
  padding: 32px 0;
  color: var(--muted);
  font-size: 14px;
  background: var(--soft);
}

@media (max-width: 840px) {
  .seo-nav__inner {
    align-items: flex-start;
    flex-direction: column;
    padding: 14px 0;
  }

  .seo-nav__links {
    flex-wrap: wrap;
  }

  .seo-hero__grid,
  .seo-grid,
  .seo-grid--two {
    grid-template-columns: 1fr;
  }

  .seo-hero__grid {
    padding: 48px 0;
  }
}