:root {
  --primary-color: #2563eb;
  --secondary-color: #1e40af;
  --bg-color: #f8fafc;
  --card-bg: #ffffff;
  --text-color: #1e293b;
  --text-muted: #64748b;
  --accent-gradient: linear-gradient(135deg, #2563eb 0%, #1d4ed8 100%);
  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
  --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
  --font-family: 'Inter', system-ui, -apple-system, sans-serif;
}

@media (prefers-color-scheme: dark) {
  :root {
    --primary-color: #60a5fa;
    --secondary-color: #3b82f6;
    --bg-color: #0f172a;
    --card-bg: #1e293b;
    --text-color: #f1f5f9;
    --text-muted: #94a3b8;
    --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.3);
    --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.3);
    --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.3);
  }
}

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

body {
  font-family: var(--font-family);
  background-color: var(--bg-color);
  background-image: linear-gradient(to bottom right, rgba(219, 234, 254, 0.7), rgba(191, 219, 254, 0.7)), url('background.png');
  background-size: cover;
  background-position: center;
  background-attachment: fixed;
  background-repeat: no-repeat;
  color: var(--text-color);
  line-height: 1.6;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

header {
  background: var(--card-bg);
  padding: 4rem 1rem;
  text-align: center;
  box-shadow: var(--shadow-sm);
  margin-bottom: 2rem;
}

h1 {
  font-size: 2.5rem;
  font-weight: 800;
  margin-bottom: 0.5rem;
  background: var(--accent-gradient);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  line-height: 1.2;
}

.subtitle {
  color: var(--text-muted);
  font-size: 1.1rem;
  max-width: 600px;
  margin: 0 auto;
}

main {
  flex: 1;
  max-width: 1200px;
  width: 100%;
  margin: 0 auto;
  padding: 0 1.5rem 4rem;
}

.category-section {
  margin-bottom: 3rem;
}

.category-title {
  font-size: 1.5rem;
  font-weight: 700;
  margin-bottom: 1.5rem;
  padding-bottom: 0.5rem;
  border-bottom: 2px solid var(--primary-color);
  display: inline-block;
}

.grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 1.5rem;
}

.card {
  background: var(--card-bg);
  border-radius: 12px;
  padding: 1.5rem;
  box-shadow: var(--shadow-sm);
  transition: transform 0.2s ease, box-shadow 0.2s ease;
  border: 1px solid transparent;
  display: flex;
  flex-direction: column;
  height: 100%;
  text-decoration: none;
  color: inherit;
}

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

.card-title {
  font-weight: 600;
  font-size: 1.125rem;
  margin-bottom: 0.5rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

/* Icons using simple CSS shapes or emojis could be added here, 
   but for now we'll stick to clean text/layout */

.card-description {
  font-size: 0.95rem;
  color: var(--text-muted);
  flex-grow: 1;
}

.card-arrow {
  margin-top: 1rem;
  font-weight: 600;
  color: var(--primary-color);
  display: flex;
  align-items: center;
  gap: 0.25rem;
  font-size: 0.9rem;
}

.card-arrow::after {
  content: "→";
  transition: transform 0.2s ease;
}

.card:hover .card-arrow::after {
  transform: translateX(4px);
}

footer {
  background: var(--card-bg);
  color: var(--text-muted);
  text-align: center;
  padding: 2rem;
  margin-top: auto;
  border-top: 1px solid rgba(0, 0, 0, 0.05);
}

footer a {
  color: var(--primary-color);
  text-decoration: none;
}

footer a:hover {
  text-decoration: underline;
}

/* Utility for external link icon if needed */
.external-link {
  display: inline-block;
  margin-left: 0.2rem;
}