header { background: #343a40; color: #fff; padding: 20px; text-align: center; }
.container { max-width: 800px; margin: auto; padding: 20px; }
.topics a { margin: 5px; display: inline-block; background: #007bff; color: #fff; padding: 10px; text-decoration: none; border-radius: 5px; }