:root {
  --primary-color: #1A237E;
  --secondary-color: #616161;
  --background-color: #FFFFFF;
  --accent-color-blue: #03A9F4;
  --accent-color-green: #8BC34A;
  --golden-ratio: 1.618;
}

body {
  font-family: 'Roboto', 'Helvetica Neue', Arial, sans-serif;
  background-color: var(--background-color);
  color: var(--secondary-color);
  line-height: 1.6;
  margin: 0;
  padding: 0;
  min-width: 320px;
  max-width: 1920px;
  margin: 0 auto;
}

.header {
  background: linear-gradient(135deg, var(--primary-color), #283593);
  color: white;
  padding: 2rem 5%;
  text-align: center;
  position: relative;
  overflow: hidden;
  margin-bottom: 3rem;
}

.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: 2.5rem;
  margin: 0;
  position: relative;
  z-index: 1;
  text-shadow: 0 2px 4px rgba(0,0,0,0.3);
}

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

.notice {
  background-color: rgba(255,255,255,0.9);
  color: var(--primary-color);
  padding: 0.5rem;
  border-radius: 4px;
  display: inline-block;
  margin-top: 1rem;
  font-size: 0.9rem;
  box-shadow: 0 2px 8px rgba(0,0,0,0.1);
}

.container {
  display: grid;
  grid-template-columns: repeat(12, 1fr);
  gap: 2rem;
  padding: 0 5%;
  margin-bottom: 3rem;
}

.sidebar {
  grid-column: 1 / 4;
  position: sticky;
  top: 2rem;
  align-self: start;
  background: rgba(255,255,255,0.9);
  border-radius: 8px;
  padding: 1.5rem;
  box-shadow: 0 4px 12px rgba(0,0,0,0.08);
}

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

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

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

.nav-menu a:hover {
  color: var(--accent-color-blue);
  background: rgba(3,169,244,0.1);
  transform: translateX(5px);
}

.nav-menu a::before {
  content: "";
  position: absolute;
  left: 0;
  top: 0;
  height: 100%;
  width: 3px;
  background: var(--accent-color-blue);
  opacity: 0;
  transition: opacity 0.3s ease;
}

.nav-menu a:hover::before {
  opacity: 1;
}

.main-content {
  grid-column: 4 / -1;
  background: white;
  border-radius: 8px;
  padding: 2rem;
  box-shadow: 0 4px 12px rgba(0,0,0,0.08);
}

article {
  max-width: 900px;
  margin: 0 auto;
}

article h2 {
  color: var(--primary-color);
  font-size: 1.8rem;
  margin-top: 2rem;
  padding-bottom: 0.5rem;
  border-bottom: 2px solid rgba(26,35,126,0.1);
}

article h3 {
  color: var(--primary-color);
  font-size: 1.5rem;
  margin-top: 1.5rem;
}

article p {
  margin: 1rem 0;
  font-size: 1.05rem;
}

pre {
  background: #f5f7fa;
  border-radius: 6px;
  padding: 1rem;
  overflow-x: auto;
  margin: 1.5rem 0;
  border-left: 4px solid var(--accent-color-blue);
}

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

table {
  width: 100%;
  border-collapse: collapse;
  margin: 1.5rem 0;
}

th, td {
  padding: 0.75rem;
  text-align: left;
  border-bottom: 1px solid #ddd;
}

th {
  background-color: rgba(26,35,126,0.05);
  color: var(--primary-color);
}

tr:hover {
  background-color: rgba(3,169,244,0.05);
}

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

.image-card {
  background: white;
  border-radius: 8px;
  overflow: hidden;
  box-shadow: 0 4px 12px 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 24px rgba(0,0,0,0.15);
}

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

.image-card .caption {
  padding: 1rem;
  font-size: 0.9rem;
  color: var(--secondary-color);
}

.footer {
  background: linear-gradient(135deg, var(--primary-color), #283593);
  color: white;
  text-align: center;
  padding: 2rem;
  margin-top: 3rem;
}

@media (max-width: 1024px) {
  .container {
    grid-template-columns: 1fr;
  }
  
  .sidebar {
    position: static;
    grid-column: 1 / -1;
  }
  
  .main-content {
    grid-column: 1 / -1;
  }
}

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

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

.fade-in {
  animation: fadeIn 0.8s ease-out forwards;
}

.delay-1 { animation-delay: 0.2s; }
.delay-2 { animation-delay: 0.4s; }
.delay-3 { animation-delay: 0.6s; }

/* Button styles */
.button {
  display: inline-block;
  background: linear-gradient(45deg, var(--accent-color-blue), var(--accent-color-green));
  color: white;
  padding: 0.8rem 1.5rem;
  border-radius: 4px;
  text-decoration: none;
  font-weight: 500;
  transition: all 0.3s ease;
  box-shadow: 0 4px 8px rgba(3,169,244,0.3);
  border: none;
  cursor: pointer;
}

.button:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 12px rgba(3,169,244,0.4);
}

/* Line illustration */
.line-illustration {
  height: 2px;
  background: linear-gradient(90deg, var(--primary-color), var(--accent-color-blue));
  margin: 2rem 0;
  position: relative;
  overflow: hidden;
}

.line-illustration::after {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: linear-gradient(90deg, transparent, rgba(255,255,255,0.8), transparent);
  animation: shine 3s infinite;
}

@keyframes shine {
  0% { transform: translateX(-100%); }
  100% { transform: translateX(100%); }
}

/* Accordion styles */
.accordion {
  margin: 1.5rem 0;
}

.accordion-item {
  border: 1px solid #ddd;
  border-radius: 4px;
  margin-bottom: 0.5rem;
  overflow: hidden;
}

.accordion-header {
  background-color: rgba(26,35,126,0.05);
  padding: 0.8rem 1rem;
  cursor: pointer;
  display: flex;
  justify-content: space-between;
  align-items: center;
  transition: background-color 0.3s ease;
}

.accordion-header:hover {
  background-color: rgba(26,35,126,0.1);
}

.accordion-content {
  padding: 0 1rem;
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.3s ease, padding 0.3s ease;
}

.accordion-item.active .accordion-content {
  padding: 1rem;
  max-height: 500px;
}

.accordion-icon {
  transition: transform 0.3s ease;
}

.accordion-item.active .accordion-icon {
  transform: rotate(180deg);
}