body {
  font-family: 'Segoe UI', sans-serif;
  margin: 0;
  padding: 0;
  background: #fefefe;
  color: #333;
}
header {
  background: #88cc88;
  padding: 1em;
  text-align: center;
}
header h1 {
  margin: 0;
}
nav a {
  margin: 0 10px;
  color: white;
  text-decoration: none;
}
main {
  padding: 2em;
}
footer {
  text-align: center;
  padding: 1em;
  background: #eee;
  margin-top: 2em;
}
.button {
  background: #4CAF50;
  padding: 1em;
  color: white;
  text-decoration: none;
  border-radius: 5px;
}
.theme-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  gap: 1em;
  list-style: none;
  padding: 0;
}
.theme-grid li {
  background: #f9f9f9;
  padding: 1em;
  border: 1px solid #ddd;
  border-radius: 5px;
}