:root {
  --color-primary: #1a73e8;
  --color-primary-hover: #1557b0;
  --color-primary-light: #e8f0fe;
  --color-bg: #ffffff;
  --color-bg-secondary: #f8f9fa;
  --color-bg-tertiary: #f1f3f4;
  --color-text: #202124;
  --color-text-secondary: #5f6368;
  --color-text-tertiary: #80868b;
  --color-border: #dadce0;
  --color-border-light: #e8eaed;
  --color-success: #34a853;
  --color-warning: #fbbc04;
  --color-error: #ea4335;
  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 16px;
  --radius-xl: 24px;
  --shadow-sm: 0 1px 3px rgba(60, 64, 67, 0.08);
  --shadow-md: 0 4px 12px rgba(60, 64, 67, 0.15);
  --shadow-lg: 0 8px 24px rgba(60, 64, 67, 0.2);
  --transition-fast: 0.2s ease;
  --transition-base: 0.3s ease;
  --transition-slow: 0.4s ease;
  --font-stack: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "PingFang SC", "Microsoft YaHei", sans-serif;
  --container-max: 1200px;
  --container-narrow: 960px;
  --space-xs: 4px;
  --space-sm: 8px;
  --space-md: 16px;
  --space-lg: 24px;
  --space-xl: 32px;
  --space-2xl: 48px;
  --space-3xl: 64px;
  --space-4xl: 96px;
}

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

html {
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--font-stack);
  color: var(--color-text);
  background-color: var(--color-bg);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

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

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

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

button {
  font-family: inherit;
  cursor: pointer;
  border: none;
  background: none;
}

ul, ol {
  list-style: none;
}

h1, h2, h3, h4, h5, h6 {
  font-weight: 600;
  line-height: 1.3;
  color: var(--color-text);
}

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

/* Utility classes */
.container {
  max-width: var(--container-max);
  margin: 0 auto;
  padding: 0 var(--space-lg);
}

.container-narrow {
  max-width: var(--container-narrow);
  margin: 0 auto;
  padding: 0 var(--space-lg);
}

.text-center {
  text-align: center;
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border-width: 0;
}

/* Spin animation */
@keyframes spin {
  from { transform: rotate(0deg); }
  to { transform: rotate(360deg); }
}

/* Fade in up animation */
@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.fade-in-up {
  animation: fadeInUp 0.6s ease forwards;
}

/* Section spacing */
.section {
  padding: var(--space-4xl) 0;
}

.section-alt {
  background-color: var(--color-bg-secondary);
}

.section-title {
  font-size: 2rem;
  margin-bottom: var(--space-md);
  text-align: center;
}

.section-subtitle {
  font-size: 1.125rem;
  color: var(--color-text-secondary);
  text-align: center;
  max-width: 600px;
  margin: 0 auto var(--space-3xl);
}

/* Badge */
.badge {
  display: inline-block;
  padding: var(--space-xs) var(--space-md);
  background-color: var(--color-primary-light);
  color: var(--color-primary);
  font-size: 0.875rem;
  font-weight: 500;
  border-radius: 100px;
}

/* Scroll reveal */
.reveal {
  opacity: 0;
  transform: translateY(24px);
  transition: opacity 0.5s ease, transform 0.5s ease;
}

.reveal.active {
  opacity: 1;
  transform: translateY(0);
}

/* Responsive typography */
@media (max-width: 768px) {
  .section {
    padding: var(--space-3xl) 0;
  }
  
  .section-title {
    font-size: 1.5rem;
  }
  
  .section-subtitle {
    font-size: 1rem;
  }
}