:root {
  --primary-color: #1e3c72;
  --secondary-color: #2a5298;
  --accent-color: #ff6600;
  --light-color: #f8f9fa;
  --dark-color: #343a40;
  --text-color: #333;
  --text-light: #fff;
  --transition: all 0.3s ease;
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: 'Roboto', sans-serif;
}

body {
  background: linear-gradient(135deg, #f5f7fa 0%, #e4e8eb 100%);
  color: var(--text-color);
  line-height: 1.6;
  font-size: 16px;
  overflow-x: hidden;
}

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

.header {
  background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
  padding: 80px 0;
  text-align: center;
  position: relative;
  overflow: hidden;
  margin-bottom: 60px;
  animation: backgroundAnimation 15s infinite alternate;
}

@keyframes backgroundAnimation {
  0% { background-position: 0% 50%; }
  100% { background-position: 100% 50%; }
}

.header::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: url('https://images.gptkong.com/demo/sample1.png') no-repeat center/cover;
  opacity: 0.1;
}

.header h1 {
  font-size: 2.5rem;
  color: var(--text-light);
  margin-bottom: 20px;
  position: relative;
  text-shadow: 0 2px 4px rgba(0,0,0,0.3);
}

.header p {
  color: rgba(255,255,255,0.9);
  max-width: 800px;
  margin: 0 auto;
  position: relative;
}

.note {
  background: rgba(255,255,255,0.2);
  backdrop-filter: blur(10px);
  padding: 15px;
  border-radius: 8px;
  margin: 30px auto;
  max-width: 800px;
  text-align: center;
  box-shadow: 0 4px 15px rgba(0,0,0,0.1);
  border: 1px solid rgba(255,255,255,0.3);
}

.note p {
  color: var(--text-light);
  font-weight: 500;
}

article {
  background: white;
  border-radius: 12px;
  box-shadow: 0 10px 30px rgba(0,0,0,0.08);
  padding: 40px;
  margin-bottom: 60px;
}

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

article h2::after {
  content: "";
  position: absolute;
  bottom: 0;
  left: 0;
  width: 80px;
  height: 4px;
  background: var(--accent-color);
  border-radius: 2px;
}

article h3 {
  color: var(--secondary-color);
  font-size: 1.5rem;
  margin: 30px 0 20px;
}

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

pre {
  background: #f5f7fa;
  border-radius: 8px;
  padding: 20px;
  margin: 25px 0;
  overflow-x: auto;
  box-shadow: inset 0 0 10px rgba(0,0,0,0.05);
  border-left: 4px solid var(--accent-color);
}

code {
  font-family: 'Courier New', monospace;
  color: #333;
}

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

.card {
  background: white;
  border-radius: 10px;
  overflow: hidden;
  box-shadow: 0 5px 15px rgba(0,0,0,0.1);
  transition: var(--transition);
}

.card:hover {
  transform: translateY(-10px);
  box-shadow: 0 15px 30px rgba(0,0,0,0.15);
}

.card img {
  width: 100%;
  height: 200px;
  object-fit: cover;
  border-bottom: 1px solid #eee;
}

.card-content {
  padding: 20px;
}

.nav-tabs {
  display: flex;
  flex-wrap: wrap;
  margin-bottom: 40px;
  border-bottom: 1px solid #ddd;
}

.nav-tabs a {
  padding: 10px 20px;
  margin-right: 10px;
  color: var(--text-color);
  text-decoration: none;
  border-radius: 5px 5px 0 0;
  transition: var(--transition);
  font-weight: 500;
}

.nav-tabs a:hover {
  background: rgba(30, 60, 114, 0.1);
}

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

.button {
  display: inline-block;
  background: var(--accent-color);
  color: white;
  padding: 12px 25px;
  border-radius: 5px;
  text-decoration: none;
  font-weight: 500;
  transition: var(--transition);
  border: none;
  cursor: pointer;
  margin: 10px 0;
}

.button:hover {
  background: #e65c00;
  transform: translateY(-2px);
  box-shadow: 0 5px 15px rgba(230, 92, 0, 0.3);
}

.footer {
  background: var(--dark-color);
  color: white;
  padding: 40px 0;
  text-align: center;
  margin-top: 60px;
}

@media (max-width: 768px) {
  .header {
    padding: 60px 0;
  }
  
  article {
    padding: 30px;
  }
  
  .grid-container {
    grid-template-columns: 1fr;
  }
}

/* Animation classes */
.fade-in {
  animation: fadeIn 1s ease-in;
}

@keyframes fadeIn {
  from { opacity: 0; }
  to { opacity: 1; }
}

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

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

/* Decorative elements */
.decorative-line {
  height: 2px;
  background: linear-gradient(90deg, transparent, var(--accent-color), transparent);
  margin: 40px 0;
  border: none;
}

.circle {
  width: 100px;
  height: 100px;
  border-radius: 50%;
  background: rgba(255, 102, 0, 0.1);
  position: absolute;
  z-index: -1;
}

.circle-1 {
  top: 20%;
  left: 10%;
  animation: float 4s ease-in-out infinite;
}

.circle-2 {
  bottom: 15%;
  right: 8%;
  width: 150px;
  height: 150px;
  animation: float 5s ease-in-out infinite reverse;
}