To set the background image of an element, use the background-image property.
Example
You can try to run the following code to learn how to work with the background-image property:
<html>
<head>
<style>
body {
background-image: url("/css/images/css.jpg");
}
</style>
<body>
<h1>Hello World!</h1>
</body>
</head>
<html>