body {
  font-family: Arial, sans-serif;
  margin: 20px;
  background-color: #f5f5f5;
  color: #000;
}

header, footer {
  background-color: #333;
  color: white;
  text-align: center;
  padding: 10px;
}

nav {
  margin: 10px 0;
}

main {
  margin: 20px 0;
}

img {
  max-width: 100%;
  height: auto;
}

@media (max-width: 600px) {
  nav {
    display: block;
    text-align: center;
  }
}