body {
  font-family: Arial, sans-serif;
  margin: 0;
  padding: 0;
  background: #f4f4f4;
}
header {
  background: #004080;
  color: #fff;
  padding: 1rem;
  text-align: center;
}
nav a {
  color: white;
  margin: 0 10px;
  text-decoration: none;
}
main {
  padding: 1rem;
}
article {
  background: white;
  padding: 1rem;
  margin-bottom: 1rem;
  border-left: 4px solid #004080;
}
footer {
  background: #333;
  color: white;
  text-align: center;
  padding: 1rem;
}
@media (max-width: 600px) {
  nav {
    display: flex;
    flex-direction: column;
    gap: 10px;
  }
}