:root {
    --primary: #001f3f;
    --secondary: #0074D9;
    --accent: #FF851B;
    --light: #f0f4f8;
    --dark: #0a192f;
    --text: #333;
    --text-light: #666;
    --shadow: 0 10px 30px rgba(0, 31, 63, 0.1);
    --transition: all 0.3s cubic-bezier(0.25, 0.8, 0.25, 1);
  }

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

  html {
    scroll-behavior: smooth;
    font-size: 16px;
  }

  body {
    font-family: 'Open Sans', sans-serif;
    line-height: 1.6;
    color: var(--text);
    background: linear-gradient(135deg, var(--light) 0%, #e0eaf1 100%);
    overflow-x: hidden;
  }

  h1, h2, h3, h4 {
    font-family: 'Montserrat', sans-serif;
    font-weight: 700;
    line-height: 1.2;
    margin-bottom: 1.5rem;
    color: var(--primary);
  }

  h2 { font-size: 2.2rem; }
  h3 { font-size: 1.8rem; }
  h4 { font-size: 1.4rem; }

  p {
    font-size: 1.1rem;
    margin-bottom: 1.5rem;
    color: var(--text-light);
  }

  a {
    text-decoration: none;
    color: var(--secondary);
    transition: var(--transition);
  }

  .container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 2rem;
  }

  .header {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 1000;
    background: rgba(255, 255, 255, 0.95);
    box-shadow: var(--shadow);
    padding: 1.5rem 0;
    transition: var(--transition);
  }

  .header.scrolled {
    padding: 1rem 0;
    background: rgba(0, 31, 63, 0.95);
  }

  .header.scrolled .nav-link {
    color: white;
  }

  .header.scrolled .logo {
    color: white;
  }

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

  .logo {
    font-size: 1.8rem;
    font-weight: 700;
    color: var(--primary);
    display: flex;
    align-items: center;
  }

  .logo-icon {
    margin-right: 0.5rem;
    font-size: 2rem;
    color: var(--accent);
  }

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

  .nav-link {
    font-weight: 600;
    font-size: 1.1rem;
    color: var(--primary);
    position: relative;
    padding: 0.5rem 0;
  }

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

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

  .hero {
    height: 100vh;
    min-height: 600px;
    display: flex;
    align-items: center;
    background: linear-gradient(rgba(0, 31, 63, 0.8), rgba(0, 31, 63, 0.8)), 
                url('https://images.gptkong.com/demo/sample1.png');
    background-size: cover;
    background-position: center;
    color: white;
    text-align: center;
    padding: 0 2rem;
    margin-bottom: 5rem;
  }

  .hero-content {
    max-width: 800px;
    margin: 0 auto;
  }

  .hero-title {
    font-size: 3.5rem;
    margin-bottom: 1.5rem;
    animation: fadeInUp 1s ease-out;
  }

  .hero-subtitle {
    font-size: 1.5rem;
    margin-bottom: 2.5rem;
    opacity: 0.9;
    animation: fadeInUp 1s ease-out 0.2s forwards;
    opacity: 0;
  }

  .btn {
    display: inline-block;
    padding: 1rem 2.5rem;
    border-radius: 50px;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 1px;
    transition: var(--transition);
    animation: fadeInUp 1s ease-out 0.4s forwards;
    opacity: 0;
  }

  .btn-primary {
    background: var(--accent);
    color: white;
    box-shadow: 0 5px 15px rgba(255, 133, 27, 0.4);
  }

  .btn-primary:hover {
    transform: translateY(-3px);
    box-shadow: 0 8px 25px rgba(255, 133, 27, 0.6);
  }

  .section {
    padding: 6rem 0;
    position: relative;
  }

  .section-title {
    text-align: center;
    margin-bottom: 4rem;
    position: relative;
  }

  .section-title::after {
    content: '';
    display: block;
    width: 80px;
    height: 4px;
    background: var(--accent);
    margin: 1.5rem auto;
    border-radius: 2px;
  }

  .section-dark {
    background: linear-gradient(135deg, var(--primary) 0%, var(--dark) 100%);
    color: white;
  }

  .section-dark .section-title,
  .section-dark h2,
  .section-dark h3,
  .section-dark h4 {
    color: white;
  }

  .section-dark p {
    color: rgba(255, 255, 255, 0.8);
  }

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

  .card {
    background: white;
    border-radius: 10px;
    overflow: hidden;
    box-shadow: var(--shadow);
    transition: var(--transition);
  }

  .card:hover {
    transform: translateY(-10px);
    box-shadow: 0 15px 35px rgba(0, 31, 63, 0.2);
  }

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

  .card-body {
    padding: 2rem;
  }

  .card-title {
    font-size: 1.4rem;
    margin-bottom: 1rem;
  }

  .feature {
    display: flex;
    gap: 2rem;
    margin-bottom: 3rem;
  }

  .feature-icon {
    flex: 0 0 80px;
    height: 80px;
    background: linear-gradient(135deg, var(--secondary) 0%, var(--primary) 100%);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    color: white;
    font-size: 2rem;
    box-shadow: 0 5px 15px rgba(0, 116, 217, 0.4);
  }

  .feature-content {
    flex: 1;
  }

  .code-block {
    background: #1e1e1e;
    color: #d4d4d4;
    border-radius: 8px;
    padding: 1.5rem;
    margin: 2rem 0;
    overflow: auto;
    font-family: 'Courier New', monospace;
    font-size: 0.95rem;
    line-height: 1.5;
  }

  .code-block code {
    display: block;
    white-space: pre;
  }

  .highlight {
    color: #569cd6;
  }

  .property {
    color: #9cdcfe;
  }

  .value {
    color: #ce9178;
  }

  .selector {
    color: #d7ba7d;
  }

  .comment {
    color: #6a9955;
  }

  .gallery {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
    gap: 1.5rem;
    margin: 3rem 0;
  }

  .gallery-item {
    border-radius: 10px;
    overflow: hidden;
    box-shadow: var(--shadow);
    transition: var(--transition);
  }

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

  .gallery-img {
    width: 100%;
    height: 200px;
    object-fit: cover;
    transition: var(--transition);
  }

  .gallery-item:hover .gallery-img {
    transform: scale(1.1);
  }

  .footer {
    background: var(--dark);
    color: white;
    padding: 4rem 0 2rem;
  }

  .footer-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 2rem;
    margin-bottom: 3rem;
  }

  .footer-title {
    font-size: 1.4rem;
    margin-bottom: 1.5rem;
    color: white;
  }

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

  .footer-link {
    margin-bottom: 0.8rem;
  }

  .footer-link a {
    color: rgba(255, 255, 255, 0.7);
    transition: var(--transition);
  }

  .footer-link a:hover {
    color: white;
    padding-left: 5px;
  }

  .copyright {
    text-align: center;
    padding-top: 2rem;
    border-top: 1px solid rgba(255, 255, 255, 0.1);
    color: rgba(255, 255, 255, 0.5);
    font-size: 0.9rem;
  }

  .back-to-top {
    position: fixed;
    bottom: 2rem;
    right: 2rem;
    width: 50px;
    height: 50px;
    background: var(--accent);
    color: white;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.5rem;
    box-shadow: 0 5px 15px rgba(255, 133, 27, 0.4);
    opacity: 0;
    visibility: hidden;
    transition: var(--transition);
    z-index: 999;
  }

  .back-to-top.active {
    opacity: 1;
    visibility: visible;
  }

  .back-to-top:hover {
    transform: translateY(-5px);
    box-shadow: 0 8px 25px rgba(255, 133, 27, 0.6);
  }

  @keyframes fadeInUp {
    from {
      opacity: 0;
      transform: translateY(20px);
    }
    to {
      opacity: 1;
      transform: translateY(0);
    }
  }

  @keyframes pulse {
    0% {
      transform: scale(1);
    }
    50% {
      transform: scale(1.05);
    }
    100% {
      transform: scale(1);
    }
  }

  @media (max-width: 992px) {
    html {
      font-size: 15px;
    }

    .hero-title {
      font-size: 3rem;
    }

    .nav {
      gap: 1.5rem;
    }
  }

  @media (max-width: 768px) {
    html {
      font-size: 14px;
    }

    .header-inner {
      flex-direction: column;
    }

    .logo {
      margin-bottom: 1rem;
    }

    .nav {
      flex-wrap: wrap;
      justify-content: center;
    }

    .hero-title {
      font-size: 2.5rem;
    }

    .hero-subtitle {
      font-size: 1.2rem;
    }

    .section {
      padding: 4rem 0;
    }
  }

  @media (max-width: 576px) {
    .hero-title {
      font-size: 2rem;
    }

    .btn {
      padding: 0.8rem 1.8rem;
    }

    .feature {
      flex-direction: column;
    }

    .feature-icon {
      margin-bottom: 1rem;
    }
  }

  .design-reference {
    position: fixed;
    bottom: 10px;
    left: 10px;
    background: rgba(0, 0, 0, 0.7);
    color: white;
    padding: 5px 10px;
    border-radius: 4px;
    font-size: 12px;
    z-index: 1000;
  }