:root {
  --primary-color: #0d6efd;
  --secondary-color: #6c757d;
  --success-color: #198754;
  --info-color: #0dcaf0;
  --warning-color: #ffc107;
  --danger-color: #dc3545;
  --light-color: #f8f9fa;
  --dark-color: #212529;
  --font-family-sans-serif: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --font-size-base: 1rem;
  --line-height-base: 1.5;
  --border-radius: 0.375rem;
  --box-shadow: 0 0.125rem 0.25rem rgba(0,0,0,0.075);
  --box-shadow-lg: 0 0.5rem 1rem rgba(0,0,0,0.15);
  --transition: all 0.3s ease;
}

[data-theme="dark"] {
  --light-color: #212529;
  --dark-color: #f8f9fa;
  --bg-color: #121212;
  --text-color: #e9ecef;
  --card-bg: #1e1e1e;
  --border-color: #333;
}

body {
  font-family: var(--font-family-sans-serif);
  font-size: var(--font-size-base);
  line-height: var(--line-height-base);
  color: var(--dark-color);
  background-color: var(--light-color);
  transition: var(--transition);
}

[data-theme="dark"] body {
  background-color: var(--bg-color);
  color: var(--text-color);
}

a {
  color: var(--primary-color);
  transition: var(--transition);
}

a:hover {
  color: var(--primary-color);
  opacity: 0.8;
  text-decoration: none;
}

.btn {
  border-radius: var(--border-radius);
  transition: var(--transition);
}

.btn:hover {
  transform: translateY(-2px);
  box-shadow: var(--box-shadow-lg);
}

.card {
  border-radius: var(--border-radius);
  transition: var(--transition);
}

[data-theme="dark"] .card {
  background-color: var(--card-bg);
  border-color: var(--border-color);
}

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

.scale-hover:hover {
  transform: scale(1.05);
}

.navbar-brand {
  font-size: 1.25rem;
  font-weight: 600;
}

.hero {
  background: linear-gradient(135deg, var(--primary-color), var(--info-color));
  color: #fff;
}

.animate-fade-in {
  animation: fadeIn 0.8s ease forwards;
  opacity: 0;
}

.delay-1 {
  animation-delay: 0.2s;
}

.delay-2 {
  animation-delay: 0.4s;
}

@keyframes fadeIn {
  to {
    opacity: 1;
  }
}

.theme-toggle {
  border: none;
  background: transparent;
  font-size: 1.2rem;
  cursor: pointer;
  transition: var(--transition);
}

.theme-toggle:hover {
  transform: rotate(20deg);
}

footer a:hover {
  opacity: 0.7;
}

@media (max-width: 576px) {
  .hero h1 {
    font-size: 2rem;
  }
  .display-4 {
    font-size: 2.5rem;
  }
}

@media (min-width: 992px) {
  .hero {
    padding: 6rem 0;
  }
}