:root {
    --primary: #1e3c72;
    --secondary: #2a5298;
    --accent: #ff7e5f;
    --text: #333;
    --light: #f8f9fa;
    --dark: #212529;
    --gradient: linear-gradient(135deg, var(--primary) 0%, var(--secondary) 100%);
  }

  * {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Helvetica Neue', Arial, sans-serif;
  }

  body {
    background-color: var(--light);
    color: var(--text);
    line-height: 1.6;
    overflow-x: hidden;
    min-height: 100%;
  }

  .header {
    background: var(--gradient);
    color: white;
    padding: 2rem 0;
    text-align: center;
    position: relative;
    overflow: hidden;
  }

  .header::before {
    content: "";
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: url('https://images.gptkong.com/demo/sample1.png') no-repeat center right;
    opacity: 0.1;
    z-index: 0;
  }

  .header-content {
    position: relative;
    z-index: 1;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 2rem;
  }

  .header h1 {
    font-size: 2.5rem;
    margin-bottom: 1rem;
    text-shadow: 0 2px 4px rgba(0,0,0,0.2);
  }

  .header p {
    font-size: 1.2rem;
    max-width: 800px;
    margin: 0 auto 2rem;
  }

  .notice {
    background: rgba(255,255,255,0.2);
    padding: 1rem;
    border-radius: 8px;
    display: inline-block;
    margin-top: 1rem;
    backdrop-filter: blur(5px);
  }

  .container {
    max-width: 1200px;
    margin: 3rem auto;
    padding: 0 2rem;
    display: grid;
    grid-template-columns: 250px 1fr;
    gap: 2rem;
  }

  .sidebar {
    position: sticky;
    top: 2rem;
    align-self: start;
    background: white;
    border-radius: 12px;
    padding: 1.5rem;
    box-shadow: 0 4px 20px rgba(0,0,0,0.08);
  }

  .sidebar h3 {
    color: var(--primary);
    margin-bottom: 1.5rem;
    padding-bottom: 0.5rem;
    border-bottom: 2px solid var(--primary);
  }

  .nav-links {
    list-style: none;
  }

  .nav-links li {
    margin-bottom: 0.8rem;
  }

  .nav-links a {
    color: var(--text);
    text-decoration: none;
    transition: all 0.3s ease;
    display: block;
    padding: 0.5rem;
    border-radius: 6px;
  }

  .nav-links a:hover {
    background: rgba(30, 60, 114, 0.1);
    color: var(--primary);
    transform: translateX(5px);
  }

  .main-content {
    background: white;
    border-radius: 12px;
    padding: 2rem;
    box-shadow: 0 4px 20px rgba(0,0,0,0.08);
  }

  article h2 {
    color: var(--primary);
    margin: 2rem 0 1.5rem;
    font-size: 1.8rem;
    position: relative;
    padding-bottom: 0.5rem;
  }

  article h2::after {
    content: "";
    position: absolute;
    bottom: 0;
    left: 0;
    width: 60px;
    height: 3px;
    background: var(--accent);
  }

  article h3 {
    color: var(--secondary);
    margin: 1.5rem 0 1rem;
    font-size: 1.4rem;
  }

  article p {
    margin-bottom: 1.5rem;
    font-size: 1.1rem;
  }

  article span {
    font-weight: 600;
    color: var(--secondary);
  }

  article color {
    background: linear-gradient(45deg, var(--accent), #feb47b);
    -webkit-background-clip: text;
    background-clip: text;
    color: transparent;
    font-weight: 600;
  }

  pre {
    background: #f5f7fa;
    border-radius: 8px;
    padding: 1.5rem;
    margin: 1.5rem 0;
    overflow: auto;
    border-left: 4px solid var(--primary);
  }

  code {
    font-family: 'Courier New', monospace;
    font-size: 0.95rem;
    color: #333;
  }

  .image-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 1.5rem;
    margin: 2rem 0;
  }

  .image-card {
    border-radius: 12px;
    overflow: hidden;
    box-shadow: 0 4px 15px rgba(0,0,0,0.1);
    transition: all 0.3s ease;
  }

  .image-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 8px 25px rgba(0,0,0,0.15);
  }

  .image-card img {
    width: 100%;
    height: auto;
    display: block;
    transition: transform 0.3s ease;
  }

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

  .footer {
    background: var(--gradient);
    color: white;
    text-align: center;
    padding: 2rem 0;
    margin-top: 3rem;
  }

  @media (max-width: 768px) {
    .container {
      grid-template-columns: 1fr;
      padding: 0 1rem;
    }

    .sidebar {
      position: static;
      margin-bottom: 2rem;
    }

    .header h1 {
      font-size: 2rem;
    }

    .header p {
      font-size: 1rem;
    }

    .image-grid {
      grid-template-columns: 1fr;
    }
  }

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

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

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