:root {
  --primary-color: #1E90FF;
  --secondary-color: #32CD32;
  --accent-color: #FF6B6B;
  --background-color: #FFFFFF;
  --text-color: #333333;
  --light-gray: #F5F7FA;
  --medium-gray: #E1E5EE;
  --dark-gray: #6B7280;
  --golden-ratio: 1.618;
}

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

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

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

.header {
  background: linear-gradient(135deg, var(--primary-color) 30%, var(--secondary-color) 90%);
  color: white;
  padding: 80px 0;
  text-align: center;
  margin-bottom: 60px;
  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 h1 {
  font-size: 2.8rem;
  margin-bottom: 20px;
  position: relative;
  z-index: 1;
  text-shadow: 0 2px 4px rgba(0,0,0,0.2);
}

.header p {
  font-size: 1.2rem;
  max-width: 800px;
  margin: 0 auto;
  position: relative;
  z-index: 1;
}

.note {
  background-color: var(--light-gray);
  padding: 15px;
  border-left: 4px solid var(--primary-color);
  margin: 40px 0;
  font-size: 0.9rem;
  color: var(--dark-gray);
}

article {
  max-width: 1000px;
  margin: 0 auto;
  padding: 0 20px;
}

article h2 {
  font-size: 2rem;
  color: var(--primary-color);
  margin: 60px 0 30px;
  padding-bottom: 15px;
  border-bottom: 2px solid var(--medium-gray);
  position: relative;
}

article h2::after {
  content: "";
  position: absolute;
  bottom: -2px;
  left: 0;
  width: 100px;
  height: 2px;
  background-color: var(--secondary-color);
}

article h3 {
  font-size: 1.5rem;
  color: var(--primary-color);
  margin: 40px 0 20px;
}

article p {
  font-size: 1.1rem;
  margin-bottom: 20px;
  line-height: 1.8;
}

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

.image-card {
  background: white;
  border-radius: 12px;
  overflow: hidden;
  box-shadow: 0 10px 20px 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 15px 30px rgba(0,0,0,0.15);
}

.image-card img {
  width: 100%;
  height: 300px;
  object-fit: cover;
  display: block;
}

.image-card .caption {
  padding: 20px;
  background: white;
}

pre {
  background: #282c34;
  color: #abb2bf;
  padding: 20px;
  border-radius: 8px;
  overflow-x: auto;
  margin: 30px 0;
  font-size: 0.95rem;
  line-height: 1.5;
  position: relative;
}

pre::before {
  content: "CSS";
  position: absolute;
  top: 0;
  left: 0;
  background: var(--primary-color);
  color: white;
  padding: 5px 15px;
  border-radius: 0 0 8px 0;
  font-size: 0.8rem;
  font-weight: bold;
}

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

.nav-tabs {
  display: flex;
  margin-bottom: 30px;
  border-bottom: 1px solid var(--medium-gray);
}

.nav-tab {
  padding: 10px 20px;
  cursor: pointer;
  border-bottom: 3px solid transparent;
  transition: all 0.3s ease;
}

.nav-tab.active {
  border-bottom-color: var(--primary-color);
  color: var(--primary-color);
  font-weight: bold;
}

.tab-content {
  display: none;
}

.tab-content.active {
  display: block;
  animation: fadeIn 0.5s ease;
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(10px); }
  to { opacity: 1; transform: translateY(0); }
}

.button {
  display: inline-block;
  padding: 12px 24px;
  background-color: var(--primary-color);
  color: white;
  border: none;
  border-radius: 6px;
  font-size: 1rem;
  cursor: pointer;
  transition: all 0.3s ease;
  text-decoration: none;
  margin: 10px 0;
}

.button:hover {
  background-color: #0d7bd4;
  transform: translateY(-2px);
  box-shadow: 0 5px 15px rgba(0,0,0,0.1);
}

.feature-box {
  background: linear-gradient(45deg, #f0f0f0, #e0e0e0);
  padding: 40px;
  border-radius: 12px;
  margin: 40px 0;
  box-shadow: 0 5px 15px rgba(0,0,0,0.05);
}

.footer {
  background-color: var(--light-gray);
  padding: 60px 0;
  margin-top: 80px;
  text-align: center;
}

.footer p {
  color: var(--dark-gray);
  font-size: 0.9rem;
}

@media (max-width: 768px) {
  .header h1 {
    font-size: 2rem;
  }
  
  article h2 {
    font-size: 1.6rem;
  }
  
  article h3 {
    font-size: 1.3rem;
  }
  
  .image-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 480px) {
  .header {
    padding: 60px 0;
  }
  
  .header h1 {
    font-size: 1.8rem;
  }
  
  article {
    padding: 0 15px;
  }
}