<!DOCTYPE html>
<html lang="en">
<head>
<title>background</title>
</head>
<body>
<button id="red">R</button>
<button id="green">G</button>
<button id="blue">B</button>
<script>
let body = document.querySelector('body');
document.querySelector('#red').addEventListener('click', function() {
body.style.backgroundColor = 'red';
});
document.querySelector('#green').addEventListener('click', function() {
body.style.backgroundColor = 'green';
});
document.querySelector('#blue').addEventListener('click', function() {
body.style.backgroundColor = 'blue';
});
</script>
</body>
</html>