<html>
<head>
<script>
function displayResult()
{
document.body.style.background="#f3f3f3 url('img_tree.png') no-repeat right top";
}
</script>
</head>
<body>
<h1>Hello World!</h1>
<br>
<button type="button" onclick="displayResult()">Set background</button>
</body>
</html>