/**
 * Modern CSS - Optimized for JinYueChen Recycling Website
 * Features: Responsive Design, Modern UI, Performance Optimized
 * Last Updated: 2025-10-19
 */

/* ============================================
   CSS VARIABLES (Custom Properties)
   ============================================ */
:root {
  /* Brand Colors */
  --primary-color: #10B981;
  --primary-dark: #059669;
  --primary-light: #34D399;
  --secondary-color: #6366F1;
  --accent-color: #F59E0B;
  
  /* Neutral Colors */
  --text-primary: #1F2937;
  --text-secondary: #6B7280;
  --text-light: #9CA3AF;
  --bg-white: #FFFFFF;
  --bg-gray-50: #F9FAFB;
  --bg-gray-100: #F3F4F6;
  --bg-gray-800: #1F2937;
  --bg-gray-900: #111827;
  
  /* Border & Shadow */
  --border-color: #E5E7EB;
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1);
  
  /* Spacing */
  --spacing-xs: 0.25rem;
  --spacing-sm: 0.5rem;
  --spacing-md: 1rem;
  --spacing-lg: 1.5rem;
  --spacing-xl: 2rem;
  --spacing-2xl: 3rem;
  
  /* Border Radius */
  --radius-sm: 0.25rem;
  --radius-md: 0.5rem;
  --radius-lg: 0.75rem;
  --radius-xl: 1rem;
  --radius-full: 9999px;
  
  /* Transitions */
  --transition-fast: 150ms ease-in-out;
  --transition-base: 250ms ease-in-out;
  --transition-slow: 350ms ease-in-out;
  
  /* Typography */
  --font-sans: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, 'Noto Sans', sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol', 'Noto Color Emoji';
  --font-mono: ui-monospace, SFMono-Regular, 'SF Mono', Menlo, Monaco, Consolas, monospace;
}

/* ============================================
   RESET & BASE STYLES
   ============================================ */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  font-size: 16px;
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-family: var(--font-sans);
  color: var(--text-primary);
  background-color: var(--bg-white);
  line-height: 1.6;
  overflow-x: hidden;
}

/* ============================================
   TYPOGRAPHY
   ============================================ */
h1, h2, h3, h4, h5, h6 {
  font-weight: 700;
  line-height: 1.2;
  margin-bottom: var(--spacing-md);
  color: var(--text-primary);
}

h1 { font-size: clamp(2rem, 5vw, 3.5rem); }
h2 { font-size: clamp(1.75rem, 4vw, 2.5rem); }
h3 { font-size: clamp(1.5rem, 3vw, 2rem); }
h4 { font-size: clamp(1.25rem, 2.5vw, 1.5rem); }
h5 { font-size: clamp(1.125rem, 2vw, 1.25rem); }
h6 { font-size: clamp(1rem, 1.5vw, 1.125rem); }

p {
  margin-bottom: var(--spacing-md);
  color: var(--text-secondary);
}

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

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

/* ============================================
   BUTTONS
   ============================================ */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0.75rem 1.5rem;
  font-size: 1rem;
  font-weight: 600;
  line-height: 1.5;
  border-radius: var(--radius-md);
  border: 2px solid transparent;
  cursor: pointer;
  transition: all var(--transition-base);
  text-decoration: none;
  white-space: nowrap;
}

.btn-primary {
  background: linear-gradient(135deg, var(--primary-color), var(--primary-dark));
  color: white;
  box-shadow: var(--shadow-md);
}

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

.btn-outline {
  background: transparent;
  color: var(--primary-color);
  border-color: var(--primary-color);
}

.btn-outline:hover {
  background: var(--primary-color);
  color: white;
}

.btn-lg {
  padding: 1rem 2rem;
  font-size: 1.125rem;
}

.btn-sm {
  padding: 0.5rem 1rem;
  font-size: 0.875rem;
}

/* ============================================
   CARDS
   ============================================ */
.card {
  background: var(--bg-white);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  overflow: hidden;
  transition: all var(--transition-base);
}

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

.card-header {
  padding: var(--spacing-lg);
  background: linear-gradient(135deg, var(--primary-color), var(--primary-dark));
  color: white;
}

.card-body {
  padding: var(--spacing-lg);
}

.card-footer {
  padding: var(--spacing-lg);
  background: var(--bg-gray-50);
  border-top: 1px solid var(--border-color);
}

/* ============================================
   LANGUAGE SWITCHER
   ============================================ */
.lang-switcher-container {
  display: flex;
  gap: 0.5rem;
  background: rgba(255, 255, 255, 0.95);
  backdrop-filter: blur(10px);
  padding: 0.5rem;
  border-radius: var(--radius-full);
  box-shadow: var(--shadow-lg);
}

.lang-switcher-container .btn {
  min-width: 50px;
  padding: 0.5rem 1rem;
  border-radius: var(--radius-full);
  font-weight: 600;
  font-size: 0.875rem;
}

.lang-switcher-container .btn.active {
  background: var(--primary-color);
  color: white;
  border-color: var(--primary-color);
}

/* ============================================
   HERO SECTION
   ============================================ */
.hero {
  position: relative;
  min-height: 600px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: linear-gradient(135deg, var(--primary-color) 0%, var(--primary-dark) 100%);
  color: white;
  overflow: hidden;
}

.hero::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: url('data:image/svg+xml,<svg width="100" height="100" xmlns="http://www.w3.org/2000/svg"><circle cx="50" cy="50" r="1" fill="white" opacity="0.1"/></svg>');
  opacity: 0.3;
}

.hero-content {
  position: relative;
  z-index: 1;
  text-align: center;
  padding: var(--spacing-2xl);
}

.hero-title {
  font-size: clamp(2.5rem, 6vw, 4rem);
  font-weight: 800;
  margin-bottom: var(--spacing-lg);
  text-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

.hero-subtitle {
  font-size: clamp(1.125rem, 2.5vw, 1.5rem);
  margin-bottom: var(--spacing-xl);
  opacity: 0.95;
}

/* ============================================
   SECTIONS
   ============================================ */
.section {
  padding: var(--spacing-2xl) 0;
}

.section-title {
  text-align: center;
  margin-bottom: var(--spacing-2xl);
  position: relative;
}

.section-title::after {
  content: '';
  display: block;
  width: 60px;
  height: 4px;
  background: var(--primary-color);
  margin: var(--spacing-md) auto 0;
  border-radius: var(--radius-full);
}

/* ============================================
   FEATURES GRID
   ============================================ */
.features-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: var(--spacing-xl);
  margin-top: var(--spacing-2xl);
}

.feature-item {
  text-align: center;
  padding: var(--spacing-xl);
  background: var(--bg-white);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  transition: all var(--transition-base);
}

.feature-item:hover {
  transform: translateY(-8px);
  box-shadow: var(--shadow-xl);
}

.feature-icon {
  width: 80px;
  height: 80px;
  margin: 0 auto var(--spacing-lg);
  background: linear-gradient(135deg, var(--primary-light), var(--primary-color));
  border-radius: var(--radius-full);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 2rem;
  color: white;
}

.feature-title {
  font-size: 1.25rem;
  font-weight: 600;
  margin-bottom: var(--spacing-sm);
}

.feature-description {
  color: var(--text-secondary);
  font-size: 0.938rem;
}

/* ============================================
   RESPONSIVE UTILITIES
   ============================================ */
@media (max-width: 768px) {
  .lang-switcher-container {
    top: 10px !important;
    right: 10px !important;
  }
  
  .hero {
    min-height: 400px;
  }
  
  .section {
    padding: var(--spacing-xl) 0;
  }
  
  .features-grid {
    grid-template-columns: 1fr;
    gap: var(--spacing-lg);
  }
}

/* ============================================
   ANIMATIONS
   ============================================ */
@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(30px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

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

/* ============================================
   LOADING STATES
   ============================================ */
.skeleton {
  background: linear-gradient(90deg, var(--bg-gray-100) 25%, var(--bg-gray-50) 50%, var(--bg-gray-100) 75%);
  background-size: 200% 100%;
  animation: loading 1.5s infinite;
}

@keyframes loading {
  0% { background-position: 200% 0; }
  100% { background-position: -200% 0; }
}

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

:focus-visible {
  outline: 2px solid var(--primary-color);
  outline-offset: 2px;
}

/* ============================================
   PRINT STYLES
   ============================================ */
@media print {
  .lang-switcher-container,
  .hero,
  nav,
  footer {
    display: none !important;
  }
  
  body {
    color: black;
    background: white;
  }
}