انها محاولة لنفسك - JavaScript Reference style

<!DOCTYPE html>
<html>
<head>
<style>
#img1 {
   position: absolute;
   left: 0px;
   top: 0px;
   z-index: -1
}
</style>
</head>
<body>

<h1>This is a Heading</h1>

<img id="img1" src="bulbon.gif" width="100" height="180">

<button type="button" onclick="myFunction()">Change stack order</button>

<p>Default z-index is 0. Z-index -1 has lower priority.</p>

<script>
function myFunction() {
   document.getElementById("img1").style.zIndex = "1";
}
</script>

</body>
</html>