:root {
  --primary-dark: #0d47a1;
  --primary-mid: #6a1b9a;
  --primary-light: #2e7d32;
  --secondary-dark: #5d4037;
  --secondary-light: #f5f5dc;
  --accent-blue: #2962ff;
  --accent-orange: #ff5722;
  --neutral-dark: #2e2e2e;
  --neutral-light: #ffffff;
}

@font-face {
  font-family: 'Roboto Slab';
  src: url('fonts/RobotoSlab-Regular.woff2') format('woff2');
}

@font-face {
  font-family: 'Open Sans';
  src: url('fonts/OpenSans-Regular.woff2') format('woff2');
}

body {
  font-family: 'Open Sans', sans-serif;
  line-height: 1.6;
  color: var(--neutral-dark);
  background: linear-gradient(135deg, #f5f7fa 0%, #e4e8eb 100%);
  margin: 0;
  padding: 0;
  min-height: 100%;
}

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

.header {
  background: linear-gradient(90deg, var(--primary-dark), var(--primary-mid));
  color: white;
  padding: 2rem 0;
  position: relative;
  overflow: hidden;
  box-shadow: 0 4px 12px rgba(0,0,0,0.1);
}

.header::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: url('https://images.gptkong.com/demo/sample1.png') no-repeat;
  background-size: cover;
  opacity: 0.1;
  z-index: 0;
}

.header-content {
  position: relative;
  z-index: 1;
  text-align: center;
}

.header h1 {
  font-family: 'Roboto Slab', serif;
  font-size: 2.5rem;
  margin-bottom: 1rem;
  text-shadow: 0 2px 4px rgba(0,0,0,0.3);
}

.header p {
  font-size: 1.2rem;
  max-width: 800px;
  margin: 0 auto 2rem;
}

.notice {
  background-color: var(--accent-orange);
  color: white;
  padding: 10px;
  text-align: center;
  font-weight: bold;
  margin-bottom: 2rem;
  border-radius: 4px;
  box-shadow: 0 2px 8px rgba(0,0,0,0.1);
}

.main-grid {
  display: grid;
  grid-template-columns: 250px 1fr;
  gap: 2rem;
  margin: 2rem 0;
}

.nav-sidebar {
  background: linear-gradient(180deg, var(--secondary-light), white);
  padding: 1.5rem;
  border-radius: 8px;
  box-shadow: 0 4px 12px rgba(0,0,0,0.08);
  position: sticky;
  top: 20px;
  align-self: start;
}

.nav-sidebar h3 {
  font-family: 'Roboto Slab', serif;
  color: var(--primary-dark);
  border-bottom: 2px solid var(--accent-blue);
  padding-bottom: 0.5rem;
  margin-top: 0;
}

.nav-links {
  list-style: none;
  padding: 0;
}

.nav-links li {
  margin-bottom: 0.8rem;
}

.nav-links a {
  color: var(--neutral-dark);
  text-decoration: none;
  display: block;
  padding: 0.5rem;
  border-radius: 4px;
  transition: all 0.3s ease;
}

.nav-links a:hover {
  background-color: rgba(41, 98, 255, 0.1);
  color: var(--accent-blue);
  transform: translateX(5px);
}

.content-area {
  background-color: white;
  padding: 2rem;
  border-radius: 8px;
  box-shadow: 0 4px 12px rgba(0,0,0,0.08);
}

article h2 {
  font-family: 'Roboto Slab', serif;
  color: var(--primary-dark);
  font-size: 1.8rem;
  margin-top: 2rem;
  padding-bottom: 0.5rem;
  border-bottom: 2px solid var(--primary-light);
}

article h3 {
  font-family: 'Roboto Slab', serif;
  color: var(--primary-mid);
  font-size: 1.5rem;
  margin-top: 1.5rem;
}

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

.image-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: 1.5rem;
  margin: 2rem 0;
}

.image-card {
  background: white;
  border-radius: 8px;
  overflow: hidden;
  box-shadow: 0 4px 8px rgba(0,0,0,0.1);
  transition: transform 0.3s ease, box-shadow 0.3s ease;
}

.image-card:hover {
  transform: translateY(-5px);
  box-shadow: 0 8px 16px rgba(0,0,0,0.15);
}

.image-card img {
  width: 100%;
  height: auto;
  display: block;
  border-radius: 8px 8px 0 0;
}

.image-caption {
  padding: 1rem;
  background: linear-gradient(180deg, var(--secondary-light), white);
}

pre {
  background: #2d2d2d;
  color: #f8f8f2;
  padding: 1.5rem;
  border-radius: 8px;
  overflow-x: auto;
  margin: 1.5rem 0;
  font-size: 0.95rem;
  line-height: 1.5;
  position: relative;
}

pre::before {
  content: "CSS";
  position: absolute;
  top: 0;
  left: 0;
  background: var(--accent-blue);
  color: white;
  padding: 0.2rem 0.8rem;
  border-radius: 0 0 4px 0;
  font-size: 0.8rem;
}

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

.footer {
  background: linear-gradient(90deg, var(--primary-dark), var(--primary-mid));
  color: white;
  padding: 2rem 0;
  text-align: center;
  margin-top: 3rem;
}

.footer p {
  margin: 0;
}

@media (max-width: 768px) {
  .main-grid {
    grid-template-columns: 1fr;
  }
  
  .nav-sidebar {
    position: static;
    margin-bottom: 2rem;
  }
  
  .header h1 {
    font-size: 2rem;
  }
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(20px); }
  to { opacity: 1; transform: translateY(0); }
}

.content-area > * {
  animation: fadeIn 0.6s ease forwards;
}

.content-area > *:nth-child(1) { animation-delay: 0.1s; }
.content-area > *:nth-child(2) { animation-delay: 0.2s; }
.content-area > *:nth-child(3) { animation-delay: 0.3s; }
.content-area > *:nth-child(4) { animation-delay: 0.4s; }
.content-area > *:nth-child(5) { animation-delay: 0.5s; }
.content-area > *:nth-child(6) { animation-delay: 0.6s; }
.content-area > *:nth-child(7) { animation-delay: 0.7s; }
.content-area > *:nth-child(8) { animation-delay: 0.8s; }
.content-area > *:nth-child(9) { animation-delay: 0.9s; }
.content-area > *:nth-child(10) { animation-delay: 1s; }