:root {
  --primary: #0A54B1;
  --secondary: #3CB371;
  --accent: #FFA500;
  --bg-light: #F9FAFB;
  --text-dark: #333;
  --text-light: #fff;
  --shadow-sm: 0 4px 6px rgba(0,0,0,0.1);
  --shadow-md: 0 6px 12px rgba(0,0,0,0.15);
  --radius: 8px;
  --transition: all 0.3s ease;
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: 'Open Sans', sans-serif;
}

body {
  background: var(--bg-light);
  color: var(--text-dark);
  line-height: 1.6;
  padding-top: 80px;
}

.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 20px;
}

/* Header Styles */
.header {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  background: linear-gradient(135deg, var(--primary), var(--secondary));
  padding: 15px 0;
  z-index: 1000;
  box-shadow: var(--shadow-sm);
}

.header-container {
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.logo {
  color: var(--text-light);
  font-size: 1.5rem;
  font-weight: 700;
  text-decoration: none;
}

.nav-links {
  display: flex;
  gap: 20px;
}

.nav-links a {
  color: var(--text-light);
  text-decoration: none;
  font-weight: 500;
  transition: var(--transition);
  padding: 5px 10px;
  border-radius: 4px;
}

.nav-links a:hover {
  background: rgba(255,255,255,0.2);
}

/* Hero Section */
.hero {
  background: linear-gradient(135deg, var(--primary), var(--secondary));
  color: var(--text-light);
  padding: 80px 0;
  margin-bottom: 60px;
  border-radius: 0 0 40px 40px;
  position: relative;
  overflow: hidden;
}

.hero::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: url('https://images.gptkong.com/demo/sample1.png') no-repeat;
  background-size: cover;
  opacity: 0.1;
}

.hero-content {
  position: relative;
  z-index: 1;
  max-width: 800px;
  margin: 0 auto;
  text-align: center;
}

.hero h1 {
  font-size: 2.5rem;
  margin-bottom: 20px;
  line-height: 1.2;
}

.hero p {
  font-size: 1.2rem;
  margin-bottom: 30px;
}

.hero-btn {
  display: inline-block;
  background: var(--accent);
  color: var(--text-dark);
  padding: 12px 30px;
  border-radius: 30px;
  text-decoration: none;
  font-weight: 600;
  transition: var(--transition);
  box-shadow: 0 4px 15px rgba(255,165,0,0.4);
}

.hero-btn:hover {
  transform: translateY(-3px);
  box-shadow: 0 6px 20px rgba(255,165,0,0.6);
}

/* Article Styles */
.article {
  background: white;
  padding: 40px;
  border-radius: var(--radius);
  box-shadow: var(--shadow-sm);
  margin-bottom: 60px;
}

.article h2 {
  color: var(--primary);
  font-size: 1.8rem;
  margin-bottom: 20px;
  position: relative;
  padding-bottom: 10px;
}

.article h2::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  width: 60px;
  height: 3px;
  background: linear-gradient(90deg, var(--primary), var(--secondary));
}

.article h3 {
  color: var(--secondary);
  font-size: 1.4rem;
  margin: 30px 0 15px;
}

.article p {
  margin-bottom: 20px;
  font-size: 1.1rem;
}

/* Code Blocks */
pre {
  background: #2d2d2d;
  color: #f8f8f2;
  padding: 20px;
  border-radius: var(--radius);
  overflow-x: auto;
  margin: 20px 0;
  box-shadow: var(--shadow-sm);
}

code {
  font-family: 'Courier New', monospace;
  font-size: 0.9rem;
}

/* Card Grid */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 30px;
  margin: 40px 0;
}

.card {
  background: white;
  border-radius: var(--radius);
  overflow: hidden;
  box-shadow: var(--shadow-sm);
  transition: var(--transition);
}

.card:hover {
  transform: translateY(-5px);
  box-shadow: var(--shadow-md);
}

.card-img {
  width: 100%;
  height: 200px;
  object-fit: cover;
}

.card-content {
  padding: 20px;
}

.card-title {
  color: var(--primary);
  font-size: 1.3rem;
  margin-bottom: 10px;
}

.card-desc {
  color: var(--text-dark);
  margin-bottom: 15px;
}

/* Timeline */
.timeline {
  position: relative;
  max-width: 800px;
  margin: 40px auto;
}

.timeline::before {
  content: '';
  position: absolute;
  top: 0;
  left: 50%;
  width: 2px;
  height: 100%;
  background: linear-gradient(to bottom, var(--primary), var(--secondary));
}

.timeline-item {
  position: relative;
  margin-bottom: 40px;
}

.timeline-content {
  width: 45%;
  padding: 20px;
  background: white;
  border-radius: var(--radius);
  box-shadow: var(--shadow-sm);
  position: relative;
}

.timeline-item:nth-child(odd) .timeline-content {
  margin-left: 55%;
}

.timeline-item:nth-child(even) .timeline-content {
  margin-right: 55%;
}

.timeline-content::after {
  content: '';
  position: absolute;
  top: 20px;
  width: 15px;
  height: 15px;
  background: var(--accent);
  border-radius: 50%;
}

.timeline-item:nth-child(odd) .timeline-content::after {
  left: -8px;
}

.timeline-item:nth-child(even) .timeline-content::after {
  right: -8px;
}

/* Footer */
.footer {
  background: linear-gradient(135deg, var(--primary), var(--secondary));
  color: var(--text-light);
  padding: 40px 0;
  text-align: center;
}

.footer p {
  margin-bottom: 20px;
}

.footer-links {
  display: flex;
  justify-content: center;
  gap: 20px;
  margin-bottom: 20px;
}

.footer-links a {
  color: var(--text-light);
  text-decoration: none;
  transition: var(--transition);
}

.footer-links a:hover {
  color: var(--accent);
}

/* Responsive */
@media (max-width: 768px) {
  .nav-links {
    display: none;
  }
  
  .hero h1 {
    font-size: 2rem;
  }
  
  .timeline::before {
    left: 30px;
  }
  
  .timeline-content,
  .timeline-item:nth-child(odd) .timeline-content,
  .timeline-item:nth-child(even) .timeline-content {
    width: calc(100% - 60px);
    margin-left: 60px;
  margin-right: 0;
  padding: 15px;
  font-size: 0.9rem;
  }
  
  .timeline-content::after {
    left: -8px;
    right: auto;
  }
}

/* Animations */
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(20px); }
  to { opacity: 1; transform: translateY(0); }
}

.scroll-animate {
  opacity: 0;
  animation: fadeIn 0.6s forwards;
}

.delay-1 { animation-delay: 0.2s; }
.delay-2 { animation-delay: 0.4s; }
.delay-3 { animation-delay: 0.6s; }

/* Utility Classes */
.text-center { text-align: center; }
.mb-20 { margin-bottom: 20px; }
.mb-40 { margin-bottom: 40px; }
.p-20 { padding: 20px; }
.bg-light { background: var(--bg-light); }