:root {
    --main-color: #1A237E;
    --accent-color: #2979FF;
    --highlight-color: #FF6D00;
    --background-color: #F5F5F5;
    --text-color: #333333;
    --card-bg: #FFFFFF;
    --shadow: 0 4px 20px rgba(0,0,0,0.08);
  }

  @font-face {
    font-family: 'Roboto';
    src: local('Roboto Bold'), local('Roboto-Bold');
    font-weight: 700;
  }

  @font-face {
    font-family: 'Open Sans';
    src: local('Open Sans Regular'), local('OpenSans-Regular');
    font-weight: 400;
  }

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

  body {
    background: var(--background-color);
    color: var(--text-color);
    font-family: 'Open Sans', sans-serif;
    line-height: 1.6;
    padding-top: 80px;
    overflow-x: hidden;
  }

  .design-notice {
    position: fixed;
    bottom: 20px;
    right: 20px;
    background: rgba(0,0,0,0.7);
    color: white;
    padding: 10px 15px;
    border-radius: 20px;
    font-size: 14px;
    z-index: 1000;
    backdrop-filter: blur(5px);
  }

  header {
    background: linear-gradient(135deg, var(--main-color) 0%, var(--accent-color) 100%);
    color: white;
    padding: 15px 5%;
    position: fixed;
    width: 100%;
    top: 0;
    box-shadow: 0 5px 15px rgba(0,0,0,0.1);
    z-index: 100;
    display: flex;
    justify-content: space-between;
    align-items: center;
  }

  .logo {
    font-family: 'Roboto', sans-serif;
    font-size: 24px;
    font-weight: 700;
    letter-spacing: 1px;
  }

  nav ul {
    display: flex;
    list-style: none;
    gap: 30px;
  }

  nav a {
    color: white;
    text-decoration: none;
    font-weight: 500;
    position: relative;
    padding: 5px 0;
    transition: all 0.3s ease;
  }

  nav a::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    width: 0;
    height: 2px;
    background: var(--highlight-color);
    transition: width 0.3s ease;
  }

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

  main {
    max-width: 1200px;
    margin: 0 auto;
    padding: 40px 5%;
  }

  .hero {
    background: linear-gradient(rgba(26,35,126,0.8), rgba(26,35,126,0.8)), url('https://images.gptkong.com/demo/sample1.png');
    background-size: cover;
    background-position: center;
    height: 400px;
    border-radius: 15px;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    text-align: center;
    color: white;
    margin-bottom: 60px;
    box-shadow: var(--shadow);
    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(255,109,0,0.2) 0%, transparent 50%);
  }

  h1, h2, h3, h4 {
    font-family: 'Roboto', sans-serif;
    font-weight: 700;
    color: var(--main-color);
    margin-bottom: 20px;
  }

  h1 {
    font-size: 2.5rem;
    line-height: 1.2;
    margin-bottom: 30px;
    position: relative;
    display: inline-block;
  }

  h1::after {
    content: '';
    position: absolute;
    bottom: -10px;
    left: 0;
    width: 60px;
    height: 4px;
    background: var(--highlight-color);
    border-radius: 2px;
  }

  h2 {
    font-size: 2rem;
    margin-top: 50px;
    padding-bottom: 15px;
    border-bottom: 1px solid rgba(0,0,0,0.1);
  }

  h3 {
    font-size: 1.5rem;
    margin-top: 40px;
  }

  p {
    margin-bottom: 20px;
    font-size: 16px;
  }

  article {
    background: white;
    border-radius: 15px;
    padding: 40px;
    box-shadow: var(--shadow);
    margin-bottom: 40px;
  }

  .card-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 30px;
    margin: 40px 0;
  }

  .card {
    background: var(--card-bg);
    border-radius: 12px;
    padding: 30px;
    box-shadow: var(--shadow);
    transition: all 0.3s ease;
    position: relative;
    overflow: hidden;
  }

  .card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 5px;
    height: 100%;
    background: var(--accent-color);
    transition: width 0.3s ease;
  }

  .card:hover {
    transform: translateY(-10px);
    box-shadow: 0 15px 30px rgba(0,0,0,0.1);
  }

  .card:hover::before {
    width: 10px;
  }

  .card img {
    width: 100%;
    height: 180px;
    object-fit: cover;
    border-radius: 8px;
    margin-bottom: 20px;
    transition: transform 0.3s ease;
  }

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

  pre {
    background: #282c34;
    color: #abb2bf;
    padding: 20px;
    border-radius: 8px;
    overflow-x: auto;
    margin: 25px 0;
    font-size: 14px;
    line-height: 1.5;
    position: relative;
  }

  pre::before {
    content: 'CSS';
    position: absolute;
    top: 0;
    left: 0;
    background: var(--accent-color);
    color: white;
    padding: 2px 10px;
    border-radius: 0 0 5px 0;
    font-size: 12px;
    font-family: 'Roboto', sans-serif;
  }

  code {
    font-family: 'Courier New', monospace;
  }

  .btn {
    display: inline-block;
    background: var(--accent-color);
    color: white;
    padding: 12px 25px;
    border-radius: 30px;
    text-decoration: none;
    font-weight: 600;
    margin-top: 15px;
    transition: all 0.3s ease;
    border: none;
    cursor: pointer;
    box-shadow: 0 4px 10px rgba(41,121,255,0.3);
  }

  .btn:hover {
    background: var(--highlight-color);
    transform: translateY(-3px);
    box-shadow: 0 6px 15px rgba(255,109,0,0.3);
  }

  .image-gallery {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
    gap: 20px;
    margin: 40px 0;
  }

  .gallery-item {
    border-radius: 10px;
    overflow: hidden;
    box-shadow: 0 5px 15px rgba(0,0,0,0.1);
    transition: all 0.3s ease;
    height: 250px;
  }

  .gallery-item:hover {
    transform: scale(1.03);
    box-shadow: 0 8px 25px rgba(0,0,0,0.15);
  }

  .gallery-item img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    transition: transform 0.5s ease;
  }

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

  footer {
    background: linear-gradient(135deg, var(--main-color) 0%, #0d1440 100%);
    color: white;
    padding: 40px 5%;
    text-align: center;
    margin-top: 80px;
  }

  .footer-links {
    display: flex;
    justify-content: center;
    gap: 30px;
    margin-bottom: 30px;
    flex-wrap: wrap;
  }

  .footer-links a {
    color: white;
    text-decoration: none;
    transition: color 0.3s ease;
  }

  .footer-links a:hover {
    color: var(--highlight-color);
  }

  .social-icons {
    display: flex;
    justify-content: center;
    gap: 20px;
    margin-bottom: 30px;
  }

  .social-icons a {
    color: white;
    font-size: 20px;
    transition: transform 0.3s ease;
  }

  .social-icons a:hover {
    transform: translateY(-5px);
    color: var(--highlight-color);
  }

  @media (max-width: 768px) {
    header {
      flex-direction: column;
      padding: 15px;
    }

    nav ul {
      margin-top: 15px;
      gap: 15px;
    }

    .hero {
      height: 300px;
    }

    h1 {
      font-size: 2rem;
    }

    h2 {
      font-size: 1.7rem;
    }

    article {
      padding: 25px;
    }

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

  @media (max-width: 480px) {
    .hero {
      height: 250px;
    }

    h1 {
      font-size: 1.8rem;
    }

    h2 {
      font-size: 1.5rem;
    }

    pre {
      padding: 15px;
      font-size: 13px;
    }
  }

  /* Animations */
  @keyframes float {
    0%, 100% {
      transform: translateY(0);
    }
    50% {
      transform: translateY(-10px);
    }
  }

  .floating {
    animation: float 3s ease-in-out infinite;
  }

  @keyframes pulse {
    0%, 100% {
      opacity: 1;
    }
    50% {
      opacity: 0.5;
    }
  }

  .pulse {
    animation: pulse 2s ease-in-out infinite;
  }

  /* Tabs */
  .tabs {
    display: flex;
    margin-bottom: -1px;
  }

  .tab {
    padding: 12px 20px;
    background: #f1f1f1;
    border: 1px solid #ddd;
    border-bottom: none;
    cursor: pointer;
    border-radius: 5px 5px 0 0;
    margin-right: 5px;
    transition: all 0.3s ease;
  }

  .tab.active {
    background: white;
    border-bottom: 1px solid white;
  }

  .tab-content {
    display: none;
    padding: 20px;
    border: 1px solid #ddd;
    border-radius: 0 5px 5px 5px;
    background: white;
  }

  .tab-content.active {
    display: block;
  }

  /* Accordion */
  .accordion {
    margin: 20px 0;
  }

  .accordion-item {
    border: 1px solid #ddd;
    border-radius: 5px;
    margin-bottom: 10px;
    overflow: hidden;
  }

  .accordion-header {
    padding: 15px;
    background: #f9f9f9;
    cursor: pointer;
    display: flex;
    justify-content: space-between;
    align-items: center;
    transition: background 0.3s ease;
  }

  .accordion-header:hover {
    background: #f1f1f1;
  }

  .accordion-content {
    padding: 0 15px;
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.3s ease, padding 0.3s ease;
  }

  .accordion-item.active .accordion-content {
    padding: 15px;
    max-height: 1000px;
  }

  /* Tooltip */
  .tooltip {
    position: relative;
    display: inline-block;
    border-bottom: 1px dotted #666;
    cursor: help;
  }

  .tooltip .tooltiptext {
    visibility: hidden;
    width: 200px;
    background-color: #333;
    color: #fff;
    text-align: center;
    border-radius: 6px;
    padding: 10px;
    position: absolute;
    z-index: 1;
    bottom: 125%;
    left: 50%;
    transform: translateX(-50%);
    opacity: 0;
    transition: opacity 0.3s;
  }

  .tooltip:hover .tooltiptext {
    visibility: visible;
    opacity: 1;
  }