:root {
    --primary: #0D2C5A;
    --secondary: #FF8F00;
    --accent: #00C4CC;
    --light: #F5F7FA;
    --dark: #1A1A2E;
    --gray: #6B7280;
    --transition: all 0.3s cubic-bezier(0.25, 0.8, 0.25, 1);
  }

  @font-face {
    font-family: 'Roboto';
    src: local('Roboto'), url(https://fonts.gstatic.com/s/roboto/v30/KFOmCnqEu92Fr1Mu4mxK.woff2) format('woff2');
    font-display: swap;
  }

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

  body {
    font-family: 'Roboto', sans-serif;
    line-height: 1.6;
    color: var(--dark);
    background: linear-gradient(135deg, var(--light) 0%, #FFFFFF 100%);
    padding: 0;
    overflow-x: hidden;
  }

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

  /* Header Styles */
  .header {
    background: linear-gradient(135deg, var(--primary) 0%, #1A365D 100%);
    color: white;
    padding: 2rem 0;
    position: relative;
    overflow: hidden;
    box-shadow: 0 4px 30px rgba(0, 0, 0, 0.1);
  }

  .header::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;
    z-index: 0;
  }

  .header-content {
    position: relative;
    z-index: 1;
    display: flex;
    flex-direction: column;
    align-items: center;
    text-align: center;
  }

  .header h1 {
    font-size: 2.5rem;
    margin-bottom: 1rem;
    text-shadow: 0 2px 4px rgba(0, 0, 0, 0.3);
    background: linear-gradient(to right, white, #E0E0E0);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
  }

  .header p {
    font-size: 1.2rem;
    max-width: 800px;
    margin-bottom: 2rem;
    opacity: 0.9;
  }

  .notice {
    background: rgba(255, 255, 255, 0.2);
    padding: 1rem;
    border-radius: 8px;
    margin-top: 2rem;
    backdrop-filter: blur(10px);
    border: 1px solid rgba(255, 255, 255, 0.1);
  }

  /* Navigation */
  .nav-tabs {
    display: flex;
    justify-content: center;
    margin: 2rem 0;
    flex-wrap: wrap;
  }

  .nav-tab {
    padding: 1rem 2rem;
    margin: 0 0.5rem;
    background: transparent;
    color: white;
    border: none;
    border-radius: 50px;
    cursor: pointer;
    font-weight: 500;
    transition: var(--transition);
    position: relative;
    overflow: hidden;
  }

  .nav-tab::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: linear-gradient(135deg, var(--secondary) 0%, #FF6B00 100%);
    z-index: -1;
    transform: translateY(100%);
    transition: var(--transition);
  }

  .nav-tab:hover::before,
  .nav-tab.active::before {
    transform: translateY(0);
  }

  /* Main Content */
  .main-content {
    padding: 3rem 0;
  }

  .content-section {
    background: white;
    border-radius: 12px;
    padding: 2.5rem;
    margin-bottom: 3rem;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.05);
    position: relative;
    overflow: hidden;
  }

  .content-section::after {
    content: '';
    position: absolute;
    top: 0;
    right: 0;
    width: 100px;
    height: 100px;
    background: url('https://images.gptkong.com/demo/sample2.png') no-repeat;
    background-size: contain;
    opacity: 0.1;
    z-index: 0;
  }

  .content-section h2 {
    color: var(--primary);
    font-size: 1.8rem;
    margin-bottom: 1.5rem;
    position: relative;
    display: inline-block;
  }

  .content-section h2::after {
    content: '';
    position: absolute;
    bottom: -10px;
    left: 0;
    width: 60px;
    height: 4px;
    background: linear-gradient(to right, var(--secondary), var(--accent));
    border-radius: 2px;
  }

  .content-section h3 {
    color: var(--primary);
    font-size: 1.4rem;
    margin: 2rem 0 1rem;
    position: relative;
    padding-left: 1rem;
  }

  .content-section h3::before {
    content: '';
    position: absolute;
    left: 0;
    top: 50%;
    transform: translateY(-50%);
    width: 4px;
    height: 60%;
    background: var(--secondary);
    border-radius: 2px;
  }

  .content-section p {
    margin-bottom: 1.5rem;
    color: var(--gray);
    font-size: 1.1rem;
    line-height: 1.8;
  }

  .content-section strong {
    color: var(--primary);
  }

  /* Code Blocks */
  pre {
    background: #1E1E1E;
    border-radius: 8px;
    padding: 1.5rem;
    margin: 2rem 0;
    overflow: auto;
    position: relative;
  }

  pre::before {
    content: 'CSS';
    position: absolute;
    top: 0;
    left: 0;
    background: var(--secondary);
    color: white;
    padding: 0.2rem 1rem;
    border-radius: 8px 0 8px 0;
    font-size: 0.8rem;
    font-weight: bold;
  }

  code {
    font-family: 'Roboto Mono', monospace;
    color: #D4D4D4;
    font-size: 0.9rem;
  }

  code .token.property {
    color: #9CDCFE;
  }

  code .token.selector {
    color: #D7BA7D;
  }

  code .token.punctuation {
    color: #D4D4D4;
  }

  code .token.value {
    color: #CE9178;
  }

  /* Image Gallery */
  .image-gallery {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 1.5rem;
    margin: 2rem 0;
  }

  .gallery-item {
    border-radius: 12px;
    overflow: hidden;
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.1);
    transition: var(--transition);
    position: relative;
  }

  .gallery-item:hover {
    transform: translateY(-5px);
    box-shadow: 0 15px 30px rgba(0, 0, 0, 0.15);
  }

  .gallery-item img {
    width: 100%;
    height: auto;
    display: block;
    transition: var(--transition);
  }

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

  /* Progress Bar */
  .progress-container {
    margin: 2rem 0;
  }

  .progress-bar {
    height: 6px;
    background: #E0E0E0;
    border-radius: 3px;
    overflow: hidden;
    margin-bottom: 1rem;
  }

  .progress-fill {
    height: 100%;
    width: 0;
    background: linear-gradient(to right, var(--secondary), var(--accent));
    transition: width 1s ease;
  }

  /* Responsive Design */
  @media (max-width: 768px) {
    .header h1 {
      font-size: 2rem;
    }

    .nav-tabs {
      flex-direction: column;
      align-items: center;
    }

    .nav-tab {
      margin: 0.5rem 0;
      width: 80%;
    }

    .content-section {
      padding: 1.5rem;
    }
  }

  @media (max-width: 480px) {
    .header h1 {
      font-size: 1.8rem;
    }

    .content-section h2 {
      font-size: 1.5rem;
    }

    .content-section h3 {
      font-size: 1.2rem;
    }

    .image-gallery {
      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 forwards;
  }

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