:root {
    --primary-color: #212B36;
    --secondary-color: #4CAF50;
    --accent-color: #FF9800;
    --background-color: #F5F5F5;
    --text-color: #444;
    --light-gray: #E0E0E0;
    --white: #FFFFFF;
    --transition: all 0.3s ease;
  }

  @font-face {
    font-family: 'Roboto';
    src: url('https://fonts.googleapis.com/css2?family=Roboto:wght@300;400;500;700&display=swap');
  }

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

  body {
    font-family: 'Roboto', sans-serif;
    background-color: var(--background-color);
    color: var(--text-color);
    line-height: 1.8;
    overflow-x: hidden;
  }

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

  /* Header Styles */
  header {
    background: linear-gradient(135deg, var(--primary-color) 0%, #2C3E50 100%);
    color: var(--white);
    padding: 20px 0;
    position: fixed;
    width: 100%;
    z-index: 1000;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
  }

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

  .logo {
    font-size: 24px;
    font-weight: 700;
    display: flex;
    align-items: center;
  }

  .logo-icon {
    width: 40px;
    height: 40px;
    margin-right: 10px;
    background-color: var(--accent-color);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
  }

  nav ul {
    display: flex;
    list-style: none;
  }

  nav ul li {
    margin-left: 30px;
  }

  nav ul li a {
    color: var(--white);
    text-decoration: none;
    font-weight: 500;
    transition: var(--transition);
    position: relative;
    padding-bottom: 5px;
  }

  nav ul li a:hover {
    color: var(--accent-color);
  }

  nav ul li a::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    width: 0;
    height: 2px;
    background-color: var(--accent-color);
    transition: var(--transition);
  }

  nav ul li a:hover::after {
    width: 100%;
  }

  .mobile-menu-btn {
    display: none;
    background: none;
    border: none;
    color: var(--white);
    font-size: 24px;
    cursor: pointer;
  }

  /* Hero Section */
  .hero {
    padding: 180px 0 100px;
    background: linear-gradient(135deg, rgba(33, 43, 54, 0.9) 0%, rgba(44, 62, 80, 0.9) 100%), 
                url('https://images.gptkong.com/demo/sample1.png') center/cover no-repeat;
    color: var(--white);
    text-align: center;
    position: relative;
    overflow: hidden;
  }

  .hero::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: radial-gradient(circle at 20% 50%, rgba(255, 152, 0, 0.2) 0%, transparent 50%);
  }

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

  .hero h1 {
    font-size: 48px;
    font-weight: 700;
    margin-bottom: 20px;
    text-shadow: 0 2px 4px rgba(0, 0, 0, 0.3);
  }

  .hero p {
    font-size: 20px;
    margin-bottom: 40px;
    opacity: 0.9;
  }

  .hero-buttons {
    display: flex;
    justify-content: center;
    gap: 20px;
  }

  .btn {
    display: inline-block;
    padding: 14px 32px;
    border-radius: 50px;
    font-weight: 500;
    text-decoration: none;
    transition: var(--transition);
    text-align: center;
  }

  .btn-primary {
    background-color: var(--accent-color);
    color: var(--white);
    box-shadow: 0 4px 12px rgba(255, 152, 0, 0.3);
  }

  .btn-primary:hover {
    background: linear-gradient(45deg, var(--accent-color), #FFA726);
    transform: translateY(-3px);
    box-shadow: 0 6px 16px rgba(255, 152, 0, 0.4);
  }

  .btn-secondary {
    background-color: transparent;
    color: var(--white);
    border: 2px solid var(--white);
  }

  .btn-secondary:hover {
    background-color: rgba(255, 255, 255, 0.1);
    transform: translateY(-3px);
  }

  /* Main Content */
  main {
    padding: 80px 0;
  }

  .section-title {
    text-align: center;
    margin-bottom: 60px;
  }

  .section-title h2 {
    font-size: 36px;
    color: var(--primary-color);
    margin-bottom: 15px;
    position: relative;
    display: inline-block;
  }

  .section-title h2::after {
    content: '';
    position: absolute;
    bottom: -10px;
    left: 50%;
    transform: translateX(-50%);
    width: 80px;
    height: 4px;
    background: linear-gradient(90deg, var(--secondary-color), var(--accent-color));
    border-radius: 2px;
  }

  .section-title p {
    font-size: 18px;
    color: var(--text-color);
    max-width: 700px;
    margin: 0 auto;
  }

  /* Article Styles */
  article {
    background-color: var(--white);
    border-radius: 12px;
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.08);
    padding: 60px;
    margin-bottom: 80px;
  }

  article h2 {
    font-size: 32px;
    color: var(--primary-color);
    margin-bottom: 30px;
    text-align: center;
    position: relative;
    padding-bottom: 15px;
  }

  article h2::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 50%;
    transform: translateX(-50%);
    width: 100px;
    height: 3px;
    background: linear-gradient(90deg, var(--secondary-color), var(--accent-color));
    border-radius: 3px;
  }

  article h3 {
    font-size: 24px;
    color: var(--secondary-color);
    margin: 40px 0 20px;
    position: relative;
    padding-left: 20px;
  }

  article h3::before {
    content: '';
    position: absolute;
    left: 0;
    top: 50%;
    transform: translateY(-50%);
    width: 8px;
    height: 8px;
    background-color: var(--accent-color);
    border-radius: 50%;
  }

  article p {
    font-size: 18px;
    line-height: 1.8;
    margin-bottom: 20px;
    color: var(--text-color);
  }

  article pre {
    background-color: #f8f9fa;
    border-radius: 8px;
    padding: 20px;
    margin: 30px 0;
    overflow-x: auto;
    box-shadow: inset 0 0 10px rgba(0, 0, 0, 0.05);
    border-left: 4px solid var(--secondary-color);
  }

  article code {
    font-family: 'Courier New', monospace;
    font-size: 16px;
    color: #333;
  }

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

  .gallery-item {
    border-radius: 12px;
    overflow: hidden;
    box-shadow: 0 6px 18px rgba(0, 0, 0, 0.1);
    transition: var(--transition);
    position: relative;
  }

  .gallery-item:hover {
    transform: translateY(-10px);
    box-shadow: 0 12px 24px rgba(0, 0, 0, 0.15);
  }

  .gallery-item img {
    width: 100%;
    height: 240px;
    object-fit: cover;
    transition: var(--transition);
  }

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

  .gallery-caption {
    position: absolute;
    bottom: 0;
    left: 0;
    right: 0;
    background: linear-gradient(transparent, rgba(0, 0, 0, 0.7));
    color: var(--white);
    padding: 20px;
  }

  .gallery-caption h4 {
    font-size: 18px;
    margin-bottom: 5px;
  }

  .gallery-caption p {
    font-size: 14px;
    opacity: 0.9;
  }

  /* Features Section */
  .features {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 40px;
    margin: 60px 0;
  }

  .feature-card {
    background-color: var(--white);
    border-radius: 12px;
    padding: 40px 30px;
    box-shadow: 0 6px 18px rgba(0, 0, 0, 0.08);
    transition: var(--transition);
    text-align: center;
    position: relative;
    overflow: hidden;
  }

  .feature-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 5px;
    background: linear-gradient(90deg, var(--secondary-color), var(--accent-color));
  }

  .feature-card:hover {
    transform: translateY(-10px);
    box-shadow: 0 12px 24px rgba(0, 0, 0, 0.12);
  }

  .feature-icon {
    width: 80px;
    height: 80px;
    margin: 0 auto 25px;
    background: linear-gradient(135deg, var(--secondary-color) 0%, #66BB6A 100%);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--white);
    font-size: 32px;
    box-shadow: 0 8px 16px rgba(76, 175, 80, 0.3);
  }

  .feature-card h3 {
    font-size: 22px;
    color: var(--primary-color);
    margin-bottom: 15px;
  }

  .feature-card p {
    font-size: 16px;
    color: var(--text-color);
  }

  /* Footer */
  footer {
    background-color: var(--primary-color);
    color: var(--white);
    padding: 60px 0 30px;
  }

  .footer-container {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 40px;
    margin-bottom: 40px;
  }

  .footer-logo {
    font-size: 24px;
    font-weight: 700;
    margin-bottom: 20px;
    display: flex;
    align-items: center;
  }

  .footer-logo-icon {
    width: 40px;
    height: 40px;
    margin-right: 10px;
    background-color: var(--accent-color);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
  }

  .footer-about p {
    font-size: 16px;
    opacity: 0.8;
    margin-bottom: 20px;
  }

  .social-links {
    display: flex;
    gap: 15px;
  }

  .social-link {
    width: 40px;
    height: 40px;
    border-radius: 50%;
    background-color: rgba(255, 255, 255, 0.1);
    display: flex;
    align-items: center;
    justify-content: center;
    transition: var(--transition);
  }

  .social-link:hover {
    background-color: var(--accent-color);
    transform: translateY(-3px);
  }

  .footer-links h3 {
    font-size: 20px;
    margin-bottom: 20px;
    position: relative;
    padding-bottom: 10px;
  }

  .footer-links h3::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    width: 40px;
    height: 3px;
    background-color: var(--accent-color);
  }

  .footer-links ul {
    list-style: none;
  }

  .footer-links li {
    margin-bottom: 12px;
  }

  .footer-links a {
    color: var(--white);
    text-decoration: none;
    opacity: 0.8;
    transition: var(--transition);
  }

  .footer-links a:hover {
    opacity: 1;
    color: var(--accent-color);
    padding-left: 5px;
  }

  .footer-bottom {
    text-align: center;
    padding-top: 30px;
    border-top: 1px solid rgba(255, 255, 255, 0.1);
  }

  .footer-bottom p {
    font-size: 14px;
    opacity: 0.7;
  }

  /* Responsive Styles */
  @media (max-width: 992px) {
    .hero h1 {
      font-size: 40px;
    }
    
    .hero p {
      font-size: 18px;
    }
    
    article {
      padding: 40px;
    }
  }

  @media (max-width: 768px) {
    nav ul {
      display: none;
    }
    
    .mobile-menu-btn {
      display: block;
    }
    
    .hero {
      padding: 150px 0 80px;
    }
    
    .hero h1 {
      font-size: 36px;
    }
    
    .hero-buttons {
      flex-direction: column;
      gap: 15px;
    }
    
    .btn {
      width: 100%;
      max-width: 300px;
      margin: 0 auto;
    }
    
    article {
      padding: 30px;
    }
    
    .section-title h2 {
      font-size: 30px;
    }
  }

  @media (max-width: 576px) {
    .hero h1 {
      font-size: 32px;
    }
    
    article {
      padding: 25px 20px;
    }
    
    article h2 {
      font-size: 28px;
    }
    
    article h3 {
      font-size: 22px;
    }
    
    .section-title h2 {
      font-size: 28px;
    }
  }

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

  .fade-in {
    animation: fadeIn 0.8s ease 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;
  }

  .mt-20 {
    margin-top: 20px;
  }

  .mt-40 {
    margin-top: 40px;
  }

  .mb-20 {
    margin-bottom: 20px;
  }

  .mb-40 {
    margin-bottom: 40px;
  }

  .py-60 {
    padding: 60px 0;
  }

  /* Reference Notice */
  .reference-notice {
    background-color: var(--primary-color);
    color: var(--white);
    padding: 15px;
    text-align: center;
    font-size: 14px;
    position: fixed;
    bottom: 0;
    left: 0;
    right: 0;
    z-index: 1000;
  }