body {
  font-family: Arial, sans-serif;
  margin: 0;
  padding: 0;
  background-color: #f0f0f0;
}

header {
  background-color: #4CAF50;
  color: white;
  padding: 1em;
  text-align: center;
}

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

nav li {
  display: inline;
  margin: 0 10px;
}

nav button {
  background: none;
  border: none;
  color: white;
  text-decoration: underline;
  cursor: pointer;
  font-size: 1em;
}

main {
  padding: 2em;
}

.content-section {
  display: none;
}

.content-section img {
  max-width: 100%;
  height: auto;
  display: block;
  margin: 20px 0;
}

footer {
  background-color: #333;
  color: white;
  text-align: center;
  padding: 1em;
  margin-top: 20px;
}