/* Responsive mobile-first styles */
body {
  margin: 0;
  font-family: sans-serif;
}

header {
  background: #333;
  color: white;
  padding: 1rem;
  text-align: center;
}

nav {
  background: #f4f4f4;
  padding: 0.5rem;
}

nav ul {
  list-style: none;
  padding: 0;
  display: flex;
  flex-wrap: wrap;
}

nav li {
  margin: 0.5rem;
}

@media (max-width: 600px) {
  nav ul {
    flex-direction: column;
  }
}