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

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
  background: linear-gradient(135deg, #66d6ea 0%, #918fff 100%);
  min-height: 100vh;
  padding: 1rem;
  line-height: 1.6;
}

.container {
  max-width: 800px;
  margin: 0 auto;
}

nav.main-nav {
  background: white;
  border-radius: 1rem;
  padding: 1rem;
  margin-bottom: 2rem;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
}

nav.main-nav ul {
  list-style: none;
  display: flex;
  gap: 1rem;
  flex-wrap: wrap;
  justify-content: center;
}

nav.main-nav a {
  padding: 0.75rem 1.5rem;
  background: #667eea;
  color: white;
  text-decoration: none;
  border-radius: 0.5rem;
  font-weight: 500;
  transition: all 0.2s;
  display: inline-block;
}

nav.main-nav a:hover {
  background: #764ba2;
  transform: translateY(-2px);
}

nav.main-nav a:focus {
  outline: 2px solid #667eea;
  outline-offset: 2px;
}

nav.main-nav a.active {
  background: #2c51f3;
}

main {
  background: white;
  border-radius: 1rem;
  box-shadow: 0 20px 60px rgba(0, 0, 0, 0.3);
  padding: 2rem;
}

h1 {
  font-size: 2rem;
  color: #2d3748;
  margin-bottom: 2rem;
  text-align: center;
}

section {
  margin-bottom: 2.5rem;
}

section:last-child {
  margin-bottom: 0;
}

h2 {
  font-size: 1.5rem;
  color: #2c51f3;
  margin-bottom: 1rem;
  padding-bottom: 0.5rem;
  border-bottom: 2px solid #e2e8f0;
}

h3 {
  font-size: 1.125rem;
  color: #4a5568;
  margin-top: 1rem;
  margin-bottom: 0.75rem;
  font-weight: 600;
}

p {
  color: #4a5568;
  margin-bottom: 1rem;
  line-height: 1.8;
}

p:last-child {
  margin-bottom: 0;
}

ul {
  list-style: none;
  padding-left: 0;
}

li {
  color: #4a5568;
  margin-bottom: 0.75rem;
  padding-left: 1.5rem;
  position: relative;
}

li:before {
  content: "▸";
  position: absolute;
  left: 0;
  color: #667eea;
  font-weight: bold;
}

.highlight {
  background: #fef3c7;
  padding: 0.2rem 0.4rem;
  border-radius: 0.25rem;
}

.section-intro {
  font-style: italic;
  color: #718096;
  margin-bottom: 1rem;
}

@media (max-width: 640px) {
  main {
    padding: 1.5rem;
  }

  h1 {
    font-size: 1.5rem;
  }

  h2 {
    font-size: 1.25rem;
  }

  nav.main-nav ul {
    flex-direction: column;
  }

  nav.main-nav a {
    width: 100%;
    text-align: center;
  }

  section {
    margin-bottom: 2rem;
  }
}

@media (min-width: 768px) {
  main {
    padding: 2.5rem;
  }
}