:root {
  --primary-blue: #4A90E2;
  --primary-green: #50E3C2;
  --neutral-grey: #F5F5F5;
  --accent-orange: #F5A623;
  --dark-bg: #1e1e1e;
  --light-text: #f5f5f5;
  --shadow-color: rgba(0,0,0,0.1);
  --transition: all 0.3s ease;
}

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

body {
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  line-height: 1.6;
  color: #333;
  background: linear-gradient(135deg, #f5f7fa 0%, #e4e8eb 100%);
  padding: 0;
  margin: 0;
  position: relative;
  overflow-x: hidden;
}

body::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: url('https://images.gptkong.com/demo/sample3.png') no-repeat center center;
  background-size: cover;
  opacity: 0.03;
  z-index: -1;
  pointer-events: none;
}

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

.header {
  text-align: center;
  padding: 40px 0;
  position: relative;
}

.header::after {
  content: "";
  display: block;
  width: 100px;
  height: 4px;
  background: linear-gradient(to right, var(--primary-blue), var(--primary-green));
  margin: 20px auto;
  border-radius: 2px;
}

.header h1 {
  font-size: 2.5rem;
  margin-bottom: 15px;
  background: linear-gradient(135deg, var(--primary-blue), var(--primary-green));
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
  text-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

.notice {
  background: rgba(255,255,255,0.9);
  padding: 15px;
  border-radius: 8px;
  margin: 20px auto;
  max-width: 800px;
  text-align: center;
  box-shadow: 0 4px 6px var(--shadow-color);
  border-left: 4px solid var(--accent-orange);
}

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

article::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 5px;
  background: linear-gradient(to right, var(--primary-blue), var(--primary-green));
}

h2, h3, h4 {
  margin: 25px 0 15px;
  color: #333;
}

h2 {
  font-size: 1.8rem;
  position: relative;
  padding-bottom: 10px;
}

h2::after {
  content: "";
  position: absolute;
  bottom: 0;
  left: 0;
  width: 60px;
  height: 3px;
  background: linear-gradient(to right, var(--primary-blue), var(--primary-green));
}

h3 {
  font-size: 1.5rem;
  color: var(--primary-blue);
}

p {
  margin-bottom: 20px;
  font-size: 1.1rem;
  line-height: 1.7;
}

.img-container {
  display: flex;
  flex-wrap: wrap;
  gap: 20px;
  margin: 30px 0;
  justify-content: center;
}

.img-card {
  width: 300px;
  height: 300px;
  border-radius: 12px;
  overflow: hidden;
  box-shadow: 0 8px 16px rgba(0,0,0,0.1);
  transition: var(--transition);
  position: relative;
}

.img-card:hover {
  transform: translateY(-10px);
  box-shadow: 0 12px 24px rgba(0,0,0,0.15);
}

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

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

pre {
  background: #282c34;
  color: #abb2bf;
  padding: 20px;
  border-radius: 8px;
  margin: 25px 0;
  overflow-x: auto;
  font-size: 0.95rem;
  line-height: 1.5;
  position: relative;
  box-shadow: 0 4px 6px rgba(0,0,0,0.1);
}

pre::before {
  content: "CSS";
  position: absolute;
  top: 0;
  left: 0;
  background: var(--primary-blue);
  color: white;
  padding: 3px 10px;
  border-radius: 0 0 5px 0;
  font-size: 0.8rem;
}

code {
  font-family: 'Courier New', Courier, monospace;
  background: rgba(74, 144, 226, 0.1);
  padding: 2px 5px;
  border-radius: 3px;
  color: var(--primary-blue);
  font-size: 0.9rem;
}

.nav-tabs {
  display: flex;
  gap: 10px;
  margin: 30px 0;
  flex-wrap: wrap;
}

.nav-tab {
  padding: 10px 20px;
  background: white;
  border-radius: 30px;
  box-shadow: 0 4px 6px var(--shadow-color);
  cursor: pointer;
  transition: var(--transition);
  font-weight: 500;
}

.nav-tab:hover {
  background: var(--primary-blue);
  color: white;
  transform: translateY(-3px);
}

.footer {
  text-align: center;
  padding: 30px;
  margin-top: 50px;
  color: #666;
  font-size: 0.9rem;
}

@media (max-width: 768px) {
  .container {
    padding: 15px;
  }
  
  article {
    padding: 25px;
  }
  
  .img-card {
    width: 100%;
    height: auto;
    max-width: 400px;
  }
  
  h2 {
    font-size: 1.5rem;
  }
  
  h3 {
    font-size: 1.3rem;
  }
}

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

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

.highlight-box {
  background: linear-gradient(135deg, rgba(74, 144, 226, 0.1), rgba(80, 227, 194, 0.1));
  border-left: 4px solid var(--primary-blue);
  padding: 20px;
  border-radius: 0 8px 8px 0;
  margin: 25px 0;
}

.toggle-content {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.3s ease;
}

.toggle-btn {
  background: var(--primary-blue);
  color: white;
  border: none;
  padding: 8px 15px;
  border-radius: 4px;
  cursor: pointer;
  display: inline-block;
  margin: 10px 0;
  transition: var(--transition);
}

.toggle-btn:hover {
  background: var(--primary-green);
}