:root {
  color-scheme: light;
  --bg: #f4f6fa;
  --card: #fff;
  --surface: #fafafa;
  --surface-subtle: #f5f5f5;
  --primary: #2459ce;
  --primary-light: #f1f6ff;
  --text: #243248;
  --text-secondary: #536176;
  --border: #dce2eb;
  --border-strong: #748196;
  --radius: 10px;
}

*, *::before, *::after { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Hiragino Kaku Gothic ProN", "Hiragino Sans", Meiryo, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.8;
  accent-color: var(--primary);
}

.header {
  background: #fff;
  border-bottom: 1px solid var(--border);
  color: var(--text);
  padding: 16px 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.header h1 { font-size: 18px; font-weight: 700; color: var(--text); margin: 0; }
.header .badge {
  background: var(--surface-subtle);
  color: var(--text-secondary);
  padding: 4px 10px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  font-size: 13px;
  font-weight: 600;
}

.container { max-width: 760px; margin: 0 auto; padding: 28px 24px; }

.intro { margin: 0 0 24px; color: var(--text-secondary); font-size: 14px; }

.cert-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
}

.cert-card {
  display: block;
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px;
  text-decoration: none;
  color: var(--text);
  min-height: 48px;
  transition: border-color 0.2s, background 0.2s;
}

.cert-card:hover,
.cert-card:focus-visible {
  border-color: var(--primary);
  background: var(--primary-light);
}

.cert-card .cert-id {
  font-size: 20px;
  font-weight: 700;
  color: var(--text);
  margin: 0 0 6px;
}

.cert-card .cert-name {
  font-size: 13px;
  color: var(--text-secondary);
  margin: 0;
  line-height: 1.5;
}

/* Modern Web Guidance: focus-visible */
:where(a, button):focus { outline: none; }
:where(a, button):focus-visible {
  outline: 2px solid var(--primary);
  outline-offset: 2px;
  border-radius: 3px;
}

/* Modern Web Guidance: text-wrap */
h1, h2 { text-wrap: balance; }

/* Visually hidden utility */
.visually-hidden:where(:not(:focus-within, :active)) {
  position: absolute !important;
  clip-path: inset(50%) !important;
  overflow: hidden !important;
  width: 1px !important;
  height: 1px !important;
  margin: -1px !important;
  padding: 0 !important;
  border: 0 !important;
  white-space: nowrap !important;
}

.site-footer {
  max-width: 760px;
  margin: 0 auto;
  padding: 24px;
  color: var(--text-secondary);
  font-size: 12px;
  border-top: 1px solid var(--border);
}

.skip-link {
  position: fixed;
  top: 8px;
  left: 8px;
  background: #333;
  color: white;
  padding: 8px 16px;
  border-radius: 6px;
  font-weight: 700;
  z-index: 9999;
  text-decoration: none;
}

@media (max-width: 600px) {
  .header { padding: 12px 16px; }
  .header h1 { font-size: 16px; }
  .container { padding: 16px; }
  .cert-grid { grid-template-columns: 1fr; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation: none !important; transition: none !important; scroll-behavior: auto !important; }
}