:root {
  /* 案A: クリーン・モダン学習系（ライトモード基調） */
  --bg-page: #f8fafc;
  --bg-subtle: #f1f5f9;
  --bg-surface: #ffffff;
  --bg-accent-soft: #eff6ff;

  /* テキストカラー */
  --text-primary: #0f172a;
  --text-secondary: #475569;
  --text-muted: #64748b;

  /* ブランド・アクセントカラー */
  --primary: #2563eb;
  --primary-dark: #1d4ed8;
  --primary-light: #dbeafe;
  --accent-sky: #0ea5e9;
  --accent-teal: #0d9488;
  --accent-amber: #f59e0b;
  --accent-amber-light: #fef3c7;
  --accent-rose: #e11d48;
  --accent-emerald: #10b981;

  /* グラデーション */
  --gradient-brand: linear-gradient(135deg, #2563eb 0%, #0ea5e9 100%);
  --gradient-warm: linear-gradient(135deg, #f59e0b 0%, #ea580c 100%);
  --gradient-hero-bg: radial-gradient(circle at 15% 20%, rgba(37, 99, 235, 0.08) 0%, transparent 45%),
                      radial-gradient(circle at 85% 30%, rgba(14, 165, 233, 0.10) 0%, transparent 50%),
                      radial-gradient(circle at 50% 80%, rgba(245, 158, 11, 0.06) 0%, transparent 50%);

  /* ボーダー・シャドウ */
  --border-color: #e2e8f0;
  --border-strong: #cbd5e1;
  --shadow-sm: 0 1px 3px rgba(15, 23, 42, 0.06), 0 1px 2px rgba(15, 23, 42, 0.04);
  --shadow-md: 0 10px 25px -5px rgba(15, 23, 42, 0.06), 0 8px 10px -6px rgba(15, 23, 42, 0.04);
  --shadow-lg: 0 20px 40px -12px rgba(15, 23, 42, 0.10);
  --shadow-primary: 0 10px 25px -5px rgba(37, 99, 235, 0.35);

  /* フォント */
  --font-family: 'Inter', 'Noto Sans JP', -apple-system, BlinkMacSystemFont, sans-serif;

  /* スペーシング */
  --spacer-sm: 0.5rem;
  --spacer-md: 1rem;
  --spacer-lg: 2rem;
  --spacer-xl: 5rem;
}

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

img {
  max-width: 100%;
  height: auto;
}

html {
  scroll-behavior: smooth;
  scroll-padding-top: 80px;
}

section[id],
[id] {
  scroll-margin-top: 80px;
}

@media (max-width: 768px) {
  html {
    scroll-padding-top: 68px;
  }
  section[id],
  [id] {
    scroll-margin-top: 68px;
  }
}

body {
  font-family: var(--font-family);
  background-color: var(--bg-page);
  background-image: var(--gradient-hero-bg);
  background-attachment: fixed;
  color: var(--text-primary);
  line-height: 1.7;
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
}

h1, h2, h3, h4 {
  font-weight: 800;
  line-height: 1.3;
  color: var(--text-primary);
  letter-spacing: -0.02em;
}

a {
  color: var(--primary);
  text-decoration: none;
  transition: all 0.25s ease;
}

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

.container {
  width: 90%;
  max-width: 1160px;
  margin: 0 auto;
}

.text-secondary {
  color: var(--text-secondary);
}

/* サーフェスカード（旧 glass-card 互換を含む） */
.glass-card,
.surface-card {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: 20px;
  padding: var(--spacer-lg);
  box-shadow: var(--shadow-md);
  transition: transform 0.3s ease, box-shadow 0.3s ease, border-color 0.3s ease;
}

.glass-card:hover,
.surface-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
  border-color: var(--border-strong);
}

/* メインボタン */
.btn-primary {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  background: var(--gradient-brand);
  color: #ffffff;
  padding: 14px 28px;
  border-radius: 9999px;
  font-weight: 700;
  font-size: 1rem;
  letter-spacing: 0.02em;
  border: none;
  cursor: pointer;
  box-shadow: var(--shadow-primary);
  transition: all 0.25s ease;
  text-align: center;
}

.btn-primary:hover {
  color: #ffffff;
  transform: translateY(-2px);
  box-shadow: 0 14px 28px -6px rgba(37, 99, 235, 0.48);
}

.btn-secondary {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  background: var(--bg-surface);
  color: var(--text-primary);
  padding: 14px 26px;
  border-radius: 9999px;
  font-weight: 700;
  font-size: 1rem;
  border: 1px solid var(--border-strong);
  cursor: pointer;
  box-shadow: var(--shadow-sm);
  transition: all 0.25s ease;
  text-align: center;
}

.btn-secondary:hover {
  color: var(--primary);
  border-color: var(--primary);
  background: var(--bg-accent-soft);
  transform: translateY(-2px);
}

/* ヘッダー・ナビゲーション */
header {
  position: fixed;
  top: 0;
  width: 100%;
  padding: 1.1rem 0;
  z-index: 1000;
  background: rgba(255, 255, 255, 0.82);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid transparent;
  transition: all 0.3s ease;
}

header.scrolled {
  background: rgba(255, 255, 255, 0.95);
  padding: 0.85rem 0;
  border-bottom: 1px solid var(--border-color);
  box-shadow: var(--shadow-sm);
}

.nav-container {
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.logo {
  display: inline-flex;
  align-items: center;
  gap: 0.65rem;
  font-size: 1.35rem;
  font-weight: 800;
  color: var(--text-primary);
  text-decoration: none;
  letter-spacing: -0.02em;
}

.logo:hover {
  color: var(--primary);
}

.logo-icon {
  width: 36px;
  height: 36px;
  border-radius: 10px;
  object-fit: cover;
  box-shadow: 0 2px 8px rgba(15, 23, 42, 0.12);
}

.logo-text {
  background: var(--gradient-brand);
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
}

.nav-links {
  display: flex;
  gap: 2rem;
  align-items: center;
}

.nav-links a {
  color: var(--text-secondary);
  font-size: 0.95rem;
  font-weight: 600;
}

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

.nav-links .nav-cta {
  background: var(--gradient-brand);
  color: #ffffff;
  padding: 8px 18px;
  border-radius: 9999px;
  font-size: 0.9rem;
  font-weight: 700;
  box-shadow: 0 4px 12px rgba(37, 99, 235, 0.25);
}

.nav-links .nav-cta:hover {
  color: #ffffff;
  transform: translateY(-1px);
  box-shadow: 0 6px 16px rgba(37, 99, 235, 0.35);
}

/* モバイルメニューボタン */
.mobile-menu-btn {
  display: none;
  background: none;
  border: 1px solid var(--border-color);
  border-radius: 10px;
  padding: 8px 10px;
  cursor: pointer;
  color: var(--text-primary);
}

/* 下層ドキュメントページ共通スタイル（terms / privacy / law） */
.doc-container {
  max-width: 840px;
  margin: 120px auto 80px;
}

.doc-title {
  font-size: 2.2rem;
  margin-bottom: 2rem;
  color: var(--text-primary);
  text-align: center;
}

.doc-content {
  padding: 3rem;
}

.doc-content h2 {
  font-size: 1.25rem;
  margin-top: 2.25rem;
  margin-bottom: 0.85rem;
  border-bottom: 2px solid var(--bg-subtle);
  padding-bottom: 0.5rem;
  color: var(--text-primary);
}

.doc-content p,
.doc-content ol,
.doc-content ul {
  color: var(--text-secondary);
  margin-bottom: 1rem;
  line-height: 1.85;
}

.doc-content ol,
.doc-content ul {
  padding-left: 1.5rem;
}

.doc-content li {
  margin-bottom: 0.6rem;
}

.doc-table {
  width: 100%;
  border-collapse: collapse;
  margin-top: 1.5rem;
}

.doc-table th,
.doc-table td {
  padding: 1.1rem 1rem;
  border-bottom: 1px solid var(--border-color);
  color: var(--text-secondary);
  text-align: left;
  line-height: 1.75;
}

.doc-table th {
  width: 34%;
  color: var(--text-primary);
  font-weight: 700;
  vertical-align: top;
  background: var(--bg-page);
  border-radius: 6px 0 0 6px;
}

.doc-table tr:last-child th,
.doc-table tr:last-child td {
  border-bottom: none;
}

/* フッター */
footer {
  background: var(--bg-surface);
  text-align: center;
  padding: 3.5rem 0 2.5rem;
  border-top: 1px solid var(--border-color);
  margin-top: var(--spacer-xl);
}

.footer-brand {
  display: inline-flex;
  align-items: center;
  gap: 0.6rem;
  margin-bottom: 1.25rem;
  font-weight: 800;
  font-size: 1.2rem;
  color: var(--text-primary);
}

.footer-links {
  display: flex;
  justify-content: center;
  gap: 2rem;
  margin-bottom: 1.5rem;
  flex-wrap: wrap;
}

.footer-links a {
  color: var(--text-secondary);
  font-size: 0.92rem;
  font-weight: 500;
}

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

/* 公式SNSリンクバー */
.footer-sns {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 0.75rem;
  margin-bottom: 1.5rem;
  flex-wrap: wrap;
}

.footer-sns-link {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  padding: 8px 15px;
  border-radius: 9999px;
  background: var(--bg-subtle);
  border: 1px solid var(--border-color);
  color: var(--text-secondary);
  font-size: 0.84rem;
  font-weight: 700;
  transition: all 0.22s ease;
}

.footer-sns-link svg {
  width: 16px;
  height: 16px;
  flex-shrink: 0;
}

.footer-sns-link:hover {
  color: var(--primary);
  background: var(--bg-accent-soft);
  border-color: rgba(37, 99, 235, 0.35);
  transform: translateY(-2px);
  box-shadow: var(--shadow-sm);
}

.copyright {
  color: var(--text-muted);
  font-size: 0.82rem;
}

/* レスポンシブ */
@media (max-width: 768px) {
  .mobile-menu-btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
  }

  .nav-links {
    display: none;
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    background: var(--bg-surface);
    flex-direction: column;
    padding: 1.25rem;
    gap: 1rem;
    border-bottom: 1px solid var(--border-color);
    box-shadow: var(--shadow-md);
  }

  .nav-links.active {
    display: flex;
  }

  .doc-content {
    padding: 1.75rem 1.25rem;
  }

  .doc-table th,
  .doc-table td {
    display: block;
    width: 100%;
  }

  .doc-table th {
    padding-bottom: 0.4rem;
    border-bottom: none;
    background: transparent;
  }

  .doc-table td {
    padding-top: 0;
  }
}