:root {
  --primary: #1E90FF;
  --secondary: #F0F0F0;
  --accent: #FF8C00;
  --text: #333333;
  --light: #FFFFFF;
  --shadow: 0 4px 20px rgba(0,0,0,0.1);
}

body {
  font-family: 'Roboto', sans-serif;
  line-height: 1.6;
  color: var(--text);
  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: var(--primary);
  color: var(--light);
  padding: 2rem 0;
  text-align: center;
  position: relative;
  overflow: hidden;
}

.header::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 5px;
  background: linear-gradient(90deg, var(--primary), var(--accent));
}

.header h1 {
  font-size: 2.5rem;
  margin: 0;
  position: relative;
  z-index: 1;
  text-shadow: 0 2px 4px rgba(0,0,0,0.2);
}

.header p {
  font-size: 1.2rem;
  opacity: 0.9;
  max-width: 800px;
  margin: 1rem auto 0;
}

.note {
  background: var(--light);
  padding: 1rem;
  border-radius: 8px;
  box-shadow: var(--shadow);
  text-align: center;
  margin: 2rem auto;
  max-width: 800px;
  border-left: 4px solid var(--accent);
}

.article-container {
  display: grid;
  grid-template-columns: 1fr 3fr;
  gap: 2rem;
  margin: 3rem 0;
}

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

.sidebar {
  background: var(--light);
  border-radius: 12px;
  padding: 1.5rem;
  box-shadow: var(--shadow);
  position: sticky;
  top: 2rem;
  align-self: start;
}

.sidebar h3 {
  color: var(--primary);
  margin-top: 0;
  border-bottom: 2px solid var(--secondary);
  padding-bottom: 0.5rem;
}

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

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

.nav-links a {
  color: var(--text);
  text-decoration: none;
  display: block;
  padding: 0.5rem;
  border-radius: 6px;
  transition: all 0.3s ease;
}

.nav-links a:hover {
  background: var(--secondary);
  color: var(--primary);
  transform: translateX(5px);
}

.article-content {
  background: var(--light);
  border-radius: 12px;
  padding: 2rem;
  box-shadow: var(--shadow);
}

.article-content h2 {
  color: var(--primary);
  font-size: 1.8rem;
  margin-top: 2rem;
  position: relative;
  padding-bottom: 0.5rem;
}

.article-content h2::after {
  content: "";
  position: absolute;
  bottom: 0;
  left: 0;
  width: 60px;
  height: 3px;
  background: linear-gradient(90deg, var(--primary), var(--accent));
}

.article-content h3 {
  color: var(--primary);
  font-size: 1.4rem;
  margin-top: 1.5rem;
}

.article-content p {
  margin: 1rem 0;
  font-size: 1.1rem;
}

.article-content ol {
  padding-left: 1.5rem;
}

.article-content ol li {
  margin-bottom: 0.8rem;
}

.article-content ol li span {
  font-weight: bold;
  color: var(--primary);
}

.color-sample {
  display: inline-block;
  width: 16px;
  height: 16px;
  border-radius: 50%;
  margin: 0 5px;
  vertical-align: middle;
  box-shadow: 0 0 0 1px rgba(0,0,0,0.1);
}

pre {
  background: #f8f8f8;
  border-radius: 8px;
  padding: 1.5rem;
  overflow-x: auto;
  margin: 1.5rem 0;
  border-left: 4px solid var(--primary);
  font-family: 'Courier New', monospace;
  font-size: 0.95rem;
  line-height: 1.5;
}

code {
  font-family: 'Courier New', monospace;
  background: #f0f0f0;
  padding: 0.2rem 0.4rem;
  border-radius: 4px;
  font-size: 0.9rem;
}

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

.image-card {
  background: var(--light);
  border-radius: 12px;
  overflow: hidden;
  box-shadow: var(--shadow);
  transition: transform 0.3s ease, box-shadow 0.3s ease;
}

.image-card:hover {
  transform: translateY(-5px);
  box-shadow: 0 8px 25px rgba(0,0,0,0.15);
}

.image-card img {
  width: 100%;
  height: auto;
  display: block;
  border-radius: 12px 12px 0 0;
}

.image-caption {
  padding: 1rem;
  text-align: center;
  background: var(--secondary);
  border-radius: 0 0 12px 12px;
}

.footer {
  background: var(--primary);
  color: var(--light);
  text-align: center;
  padding: 2rem 0;
  margin-top: 3rem;
}

.footer p {
  margin: 0;
  opacity: 0.8;
}

@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(30,144,255,0.1) 0%, rgba(255,140,0,0.1) 100%);
  border-radius: 12px;
  padding: 1.5rem;
  margin: 2rem 0;
  border-left: 4px solid var(--accent);
}

.toggle-content {
  margin: 1.5rem 0;
}

.toggle-btn {
  background: var(--primary);
  color: var(--light);
  border: none;
  padding: 0.8rem 1.5rem;
  border-radius: 6px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: space-between;
  width: 100%;
  font-size: 1.1rem;
  transition: all 0.3s ease;
}

.toggle-btn:hover {
  background: #1a7fd9;
}

.toggle-btn::after {
  content: "+";
  font-size: 1.5rem;
  transition: transform 0.3s ease;
}

.toggle-btn.active::after {
  transform: rotate(45deg);
}

.toggle-panel {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.3s ease;
  background: var(--light);
  border-radius: 0 0 8px 8px;
  box-shadow: 0 4px 8px rgba(0,0,0,0.1);
}

.toggle-panel.active {
  max-height: 1000px;
  padding: 1.5rem;
}