:root {
  --color-primary: #7B61FF;
  --color-primary-dark: #6a4dd6;
  --color-bg: #ffffff;
  --color-bg-alt: #f8f9fa;
  --color-text: #1a1a1a;
  --color-text-secondary: #666666;
  --color-border: #e0e0e0;

  --spacing-xs: 0.25rem;
  --spacing-sm: 0.5rem;
  --spacing-md: 1rem;
  --spacing-lg: 1.5rem;
  --spacing-xl: 2rem;

  --radius-sm: 0.375rem;
  --radius-md: 0.5rem;
  --radius-lg: 0.75rem;

  --font-sans: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Hiragino Sans',
    'Noto Sans JP', 'Segoe UI', Roboto, sans-serif;
}

* {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  padding: 0;
  font-family: var(--font-sans);
  background-color: var(--color-bg);
  color: var(--color-text);
  line-height: 1.6;
}

/* Header */
header {
  background-color: var(--color-bg-alt);
  border-bottom: 1px solid var(--color-border);
  padding: var(--spacing-xl);
  margin-bottom: var(--spacing-xl);
}

header h1 {
  margin: 0 0 var(--spacing-md) 0;
  font-size: 2rem;
  color: var(--color-primary);
}

header h1 small {
  display: block;
  font-size: 0.9rem;
  color: var(--color-text-secondary);
  font-weight: normal;
  margin-top: var(--spacing-xs);
}

.site-description {
  margin: 0 0 var(--spacing-lg) 0;
  font-size: 0.95rem;
  color: var(--color-text-secondary);
  line-height: 1.6;
}

nav {
  display: flex;
  gap: var(--spacing-md);
  flex-wrap: wrap;
}

nav button {
  padding: var(--spacing-sm) var(--spacing-md);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-md);
  background-color: var(--color-bg);
  color: var(--color-text);
  cursor: pointer;
  font-size: 0.95rem;
  font-weight: 500;
  transition: all 0.2s ease;
}

nav button:hover {
  border-color: var(--color-primary);
  color: var(--color-primary);
}

nav button.active {
  background-color: var(--color-primary);
  border-color: var(--color-primary);
  color: white;
}

/* Main content */
main {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 var(--spacing-lg);
  min-height: calc(100vh - 300px);
}

#article-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: var(--spacing-lg);
  margin-bottom: var(--spacing-xl);
}

/* Article card */
.article-card {
  display: flex;
  flex-direction: column;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  overflow: hidden;
  text-decoration: none;
  color: inherit;
  background-color: var(--color-bg);
  transition: all 0.2s ease;
  cursor: pointer;
}

.article-card:hover {
  border-color: var(--color-primary);
  box-shadow: 0 4px 12px rgba(123, 97, 255, 0.1);
}

.card-thumbnail {
  width: 100%;
  aspect-ratio: 16 / 9;
  overflow: hidden;
  background-color: var(--color-bg-alt);
  flex-shrink: 0;
}

.card-thumbnail img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  display: block;
}

.card-body {
  padding: var(--spacing-lg);
  display: flex;
  flex-direction: column;
  flex: 1;
}

.article-card h2 {
  margin: var(--spacing-md) 0;
  font-size: 1.2rem;
  line-height: 1.4;
}

.article-card .summary {
  color: var(--color-text-secondary);
  font-size: 0.95rem;
  margin: var(--spacing-md) 0;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.article-card time {
  display: block;
  color: var(--color-text-secondary);
  font-size: 0.85rem;
  margin-top: var(--spacing-md);
}

/* Category badge */
.category-badge {
  display: inline-block;
  padding: var(--spacing-xs) var(--spacing-sm);
  border-radius: var(--radius-sm);
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  margin-bottom: var(--spacing-sm);
}

.category-beginner {
  background-color: #e3f2fd;
  color: #1565c0;
}

.category-tutorial {
  background-color: #f3e5f5;
  color: #6a1b9a;
}

.category-news {
  background-color: #fff3e0;
  color: #e65100;
}

.category-feature {
  background-color: #e8f5e9;
  color: #2e7d32;
}

/* Source badge */
.source-badge {
  display: inline-block;
  font-size: 0.7rem;
  padding: var(--spacing-xs) var(--spacing-sm);
  background-color: var(--color-bg-alt);
  border-radius: var(--radius-sm);
  margin-left: var(--spacing-md);
  color: var(--color-text-secondary);
}

/* Load more button */
#load-more {
  display: block;
  margin: var(--spacing-xl) auto;
  padding: var(--spacing-md) var(--spacing-xl);
  background-color: var(--color-primary);
  color: white;
  border: none;
  border-radius: var(--radius-md);
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: background-color 0.2s ease;
}

#load-more:hover {
  background-color: var(--color-primary-dark);
}

#load-more:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

/* Footer */
footer {
  border-top: 1px solid var(--color-border);
  margin-top: var(--spacing-xl);
  padding-top: var(--spacing-lg);
  text-align: center;
  color: var(--color-text-secondary);
  font-size: 0.9rem;
}

/* Empty state */
.empty-state {
  text-align: center;
  padding: var(--spacing-xl);
  color: var(--color-text-secondary);
}

/* Responsive */
@media (max-width: 640px) {
  header {
    padding: var(--spacing-lg);
  }

  header h1 {
    font-size: 1.5rem;
  }

  main {
    padding: 0 var(--spacing-md);
  }

  #article-grid {
    grid-template-columns: 1fr;
    gap: var(--spacing-md);
  }

  nav {
    flex-direction: column;
  }

  nav button {
    width: 100%;
  }
}

/* Loading animation */
.loading {
  display: inline-block;
  width: 20px;
  height: 20px;
  border: 3px solid var(--color-border);
  border-top-color: var(--color-primary);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}

@keyframes spin {
  to {
    transform: rotate(360deg);
  }
}