:root {
  --primary-color: #003366;
  --secondary-color: #ffffff;
  --accent-color: #28a745;
  --highlight-color: #fd7e14;
  --bg-gradient: linear-gradient(135deg, #f0f4f8, #d9e2ec);
  --card-shadow: 0 10px 30px rgba(0, 51, 102, 0.1);
  --transition: all 0.3s cubic-bezier(0.25, 0.8, 0.25, 1);
}

body {
  margin: 0;
  padding: 0;
  font-family: 'Roboto', 'Helvetica Neue', Arial, sans-serif;
  line-height: 1.6;
  color: #333;
  background: var(--bg-gradient);
  overflow-x: hidden;
}

.header {
  position: relative;
  height: 80vh;
  min-height: 500px;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  text-align: center;
  padding: 0 20px;
  background: linear-gradient(rgba(0, 51, 102, 0.8), rgba(0, 51, 102, 0.8)), 
              url('https://images.gptkong.com/demo/sample1.png') center/cover no-repeat;
  color: white;
  clip-path: polygon(0 0, 100% 0, 100% 85%, 0 100%);
  margin-bottom: 5rem;
}

.header::after {
  content: '';
  position: absolute;
  bottom: -50px;
  left: 0;
  width: 100%;
  height: 100px;
  background: url('data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHZpZXdCb3g9IjAgMCAxNDQwIDMyMCI+PHBhdGggZmlsbD0iI2YwZjRmOCIgZmlsbC1vcGFjaXR5PSIxIiBkPSJNMCwxNjBMMTYwLDMyMEgxNDQwVjBIMTYwTDAsMTYweiIvPjwvc3ZnPg==') center/cover no-repeat;
  z-index: 10;
}

.header h1 {
  font-size: 3.5rem;
  margin-bottom: 1.5rem;
  text-shadow: 0 5px 15px rgba(0, 0, 0, 0.3);
  animation: fadeInDown 1s ease;
}

.header p {
  font-size: 1.5rem;
  max-width: 800px;
  margin-bottom: 2rem;
  animation: fadeInUp 1s ease;
}

.notice {
  position: fixed;
  bottom: 20px;
  right: 20px;
  background: rgba(0, 0, 0, 0.7);
  color: white;
  padding: 10px 20px;
  border-radius: 5px;
  z-index: 1000;
  font-size: 0.9rem;
}

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

article {
  background: white;
  border-radius: 10px;
  box-shadow: var(--card-shadow);
  padding: 3rem;
  margin: 3rem auto;
  position: relative;
  overflow: hidden;
}

article::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  width: 5px;
  height: 100%;
  background: var(--primary-color);
}

article h2 {
  color: var(--primary-color);
  font-size: 2.5rem;
  margin-bottom: 2rem;
  position: relative;
  padding-bottom: 1rem;
}

article h2::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  width: 100px;
  height: 4px;
  background: linear-gradient(to right, var(--primary-color), var(--accent-color));
}

article h3 {
  color: var(--primary-color);
  font-size: 1.8rem;
  margin: 2.5rem 0 1.5rem;
  position: relative;
}

article p {
  font-size: 1.1rem;
  line-height: 1.8;
  margin-bottom: 1.5rem;
}

pre {
  background: #f5f7fa;
  border-radius: 8px;
  padding: 1.5rem;
  overflow: auto;
  margin: 2rem 0;
  border-left: 4px solid var(--primary-color);
  position: relative;
}

pre::before {
  content: 'CSS';
  position: absolute;
  top: 0;
  right: 0;
  background: var(--primary-color);
  color: white;
  padding: 0.2rem 0.8rem;
  font-size: 0.8rem;
  border-bottom-left-radius: 5px;
}

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

.gallery {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: 2rem;
  margin: 3rem 0;
}

.gallery img {
  width: 100%;
  height: 300px;
  object-fit: cover;
  border-radius: 10px;
  box-shadow: 0 5px 15px rgba(0, 0, 0, 0.1);
  transition: var(--transition);
}

.gallery img:hover {
  transform: translateY(-10px);
  box-shadow: 0 15px 30px rgba(0, 0, 0, 0.2);
}

ol {
  counter-reset: item;
  padding-left: 0;
}

ol li {
  display: flex;
  align-items: flex-start;
  margin-bottom: 1.5rem;
  list-style-type: none;
  position: relative;
  padding-left: 3rem;
}

ol li::before {
  content: counter(item);
  counter-increment: item;
  position: absolute;
  left: 0;
  top: 0;
  background: var(--primary-color);
  color: white;
  width: 2rem;
  height: 2rem;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: bold;
}

ol li span {
  font-weight: bold;
  color: var(--primary-color);
  margin-right: 0.5rem;
}

.nav-tabs {
  display: flex;
  flex-wrap: wrap;
  margin: 2rem 0;
  border-bottom: 1px solid #eee;
}

.nav-tabs a {
  padding: 1rem 2rem;
  margin-right: 0.5rem;
  background: #f5f7fa;
  color: var(--primary-color);
  text-decoration: none;
  border-radius: 5px 5px 0 0;
  transition: var(--transition);
  font-weight: 500;
}

.nav-tabs a:hover {
  background: #e1e5eb;
}

.nav-tabs a.active {
  background: var(--primary-color);
  color: white;
}

.card {
  background: white;
  border-radius: 10px;
  box-shadow: var(--card-shadow);
  overflow: hidden;
  margin: 2rem 0;
  transition: var(--transition);
}

.card:hover {
  transform: translateY(-5px);
  box-shadow: 0 15px 30px rgba(0, 51, 102, 0.2);
}

.card-header {
  background: var(--primary-color);
  color: white;
  padding: 1.5rem;
  font-size: 1.2rem;
  font-weight: bold;
  cursor: pointer;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.card-header::after {
  content: '+';
  font-size: 1.5rem;
  transition: var(--transition);
}

.card-header.active::after {
  content: '-';
}

.card-content {
  padding: 0;
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.5s ease;
}

.card-content.active {
  padding: 1.5rem;
  max-height: 1000px;
}

.footer {
  background: var(--primary-color);
  color: white;
  padding: 3rem 0;
  text-align: center;
  margin-top: 5rem;
}

.footer p {
  margin: 0;
}

@keyframes fadeInDown {
  from {
    opacity: 0;
    transform: translateY(-30px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(30px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@media (max-width: 768px) {
  .header h1 {
    font-size: 2.5rem;
  }
  
  .header p {
    font-size: 1.2rem;
  }
  
  article {
    padding: 2rem;
  }
  
  article h2 {
    font-size: 2rem;
  }
  
  article h3 {
    font-size: 1.5rem;
  }
  
  .gallery {
    grid-template-columns: 1fr;
  }
}