:root {
    --primary: #2c3e50;
    --secondary: #8e44ad;
    --accent: #3498db;
    --light: #ecf0f1;
    --dark: #1a1a1a;
    --text: #333333;
    --white: #ffffff;
    --gradient: linear-gradient(135deg, var(--primary), var(--secondary));
  }

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

  body {
    font-family: 'Roboto', sans-serif;
    color: var(--text);
    background-color: var(--light);
    line-height: 1.6;
    overflow-x: hidden;
  }

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

  header {
    background: var(--gradient);
    color: var(--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') center/cover no-repeat;
    opacity: 0.1;
    z-index: 0;
  }

  .header-content {
    position: relative;
    z-index: 1;
  }

  h1, h2, h3, h4 {
    font-family: 'Exo', sans-serif;
    margin-bottom: 1.5rem;
    color: var(--primary);
  }

  h1 {
    font-size: 2.5rem;
    background: linear-gradient(90deg, var(--white), var(--accent));
    -webkit-background-clip: text;
    background-clip: text;
    color: transparent;
    text-shadow: 0 2px 4px rgba(0,0,0,0.1);
  }

  h2 {
    font-size: 2rem;
    color: var(--secondary);
    position: relative;
    padding-bottom: 0.5rem;
  }

  h2::after {
    content: "";
    position: absolute;
    bottom: 0;
    left: 0;
    width: 100px;
    height: 3px;
    background: var(--gradient);
  }

  h3 {
    font-size: 1.5rem;
    color: var(--primary);
  }

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

  .nav {
    position: sticky;
    top: 0;
    background: rgba(44, 62, 80, 0.95);
    backdrop-filter: blur(10px);
    padding: 1rem 0;
    z-index: 1000;
    box-shadow: 0 4px 12px rgba(0,0,0,0.1);
  }

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

  .nav-links {
    display: flex;
    gap: 2rem;
  }

  .nav-link {
    color: var(--white);
    text-decoration: none;
    font-weight: 500;
    transition: all 0.3s ease;
    position: relative;
  }

  .nav-link::after {
    content: "";
    position: absolute;
    bottom: -5px;
    left: 0;
    width: 0;
    height: 2px;
    background: var(--accent);
    transition: width 0.3s ease;
  }

  .nav-link:hover::after {
    width: 100%;
  }

  .nav-link:hover {
    color: var(--accent);
  }

  .reference {
    background: var(--light);
    padding: 1rem;
    border-radius: 8px;
    margin: 2rem 0;
    text-align: center;
    font-style: italic;
    border-left: 4px solid var(--accent);
  }

  article {
    background: var(--white);
    padding: 3rem;
    margin: 3rem 0;
    border-radius: 12px;
    box-shadow: 0 10px 30px rgba(0,0,0,0.05);
  }

  .article-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: 3rem;
  }

  .section {
    margin-bottom: 3rem;
  }

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

  .image-card {
    border-radius: 12px;
    overflow: hidden;
    box-shadow: 0 8px 16px rgba(0,0,0,0.1);
    transition: transform 0.3s ease, box-shadow 0.3s ease;
  }

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

  .image-card img {
    width: 100%;
    height: auto;
    display: block;
  }

  pre {
    background: #282c34;
    color: #abb2bf;
    padding: 1.5rem;
    border-radius: 8px;
    overflow-x: auto;
    margin: 1.5rem 0;
    font-family: 'Fira Code', monospace;
    font-size: 0.9rem;
    line-height: 1.5;
    position: relative;
  }

  pre::before {
    content: "CSS";
    position: absolute;
    top: 0;
    right: 0;
    background: var(--secondary);
    color: white;
    padding: 0.2rem 0.8rem;
    font-size: 0.8rem;
    border-radius: 0 0 0 8px;
  }

  code {
    font-family: 'Fira Code', monospace;
    background: rgba(142, 68, 173, 0.1);
    padding: 0.2rem 0.4rem;
    border-radius: 4px;
    color: var(--secondary);
  }

  .color-sample {
    display: inline-block;
    width: 20px;
    height: 20px;
    border-radius: 50%;
    vertical-align: middle;
    margin: 0 5px;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
  }

  .portal-container {
    display: flex;
    justify-content: center;
    margin: 3rem 0;
  }

  .portal {
    width: 200px;
    height: 200px;
    background: linear-gradient(45deg, var(--primary), var(--secondary));
    border-radius: 50%;
    display: flex;
    justify-content: center;
    align-items: center;
    box-shadow: 0 0 30px rgba(142, 68, 173, 0.5);
    animation: pulse 4s infinite alternate;
    cursor: pointer;
    transition: transform 1s ease;
  }

  @keyframes pulse {
    0% { box-shadow: 0 0 30px rgba(142, 68, 173, 0.5); }
    100% { box-shadow: 0 0 50px rgba(142, 68, 173, 0.8); }
  }

  .portal:hover {
    transform: rotateY(180deg);
  }

  .button-demo {
    display: inline-block;
    background: var(--gradient);
    color: white;
    padding: 12px 24px;
    border-radius: 30px;
    text-decoration: none;
    font-weight: 500;
    margin: 1rem 0;
    box-shadow: 0 4px 6px rgba(0,0,0,0.1);
    transition: all 0.3s ease;
    border: none;
    cursor: pointer;
  }

  .button-demo:hover {
    transform: translateY(-3px);
    box-shadow: 0 8px 15px rgba(0,0,0,0.2);
  }

  .chart-container {
    width: 100%;
    height: 300px;
    background: var(--light);
    border-radius: 8px;
    padding: 20px;
    margin: 2rem 0;
    display: flex;
    align-items: flex-end;
    justify-content: space-around;
  }

  .bar {
    width: 40px;
    background: var(--gradient);
    border-radius: 4px 4px 0 0;
    animation: grow 2s ease forwards;
  }

  @keyframes grow {
    from { height: 0; }
    to { height: 100%; }
  }

  footer {
    background: var(--dark);
    color: var(--white);
    padding: 3rem 0;
    text-align: center;
  }

  .footer-links {
    display: flex;
    justify-content: center;
    gap: 2rem;
    margin: 1.5rem 0;
  }

  .footer-link {
    color: var(--white);
    text-decoration: none;
    transition: color 0.3s ease;
  }

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

  @media (max-width: 768px) {
    .nav-container {
      flex-direction: column;
      gap: 1rem;
    }

    .nav-links {
      flex-direction: column;
      gap: 1rem;
      align-items: center;
    }

    article {
      padding: 2rem;
    }

    h1 {
      font-size: 2rem;
    }

    h2 {
      font-size: 1.5rem;
    }
  }

  @media (max-width: 480px) {
    article {
      padding: 1.5rem;
    }

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