Tryit Editor v2.9

Edit This Code:
<!DOCTYPE html>
<html>
<head>
<style> 
#myDIV {
    position: absolute;
    width: 300px;
    height: 150px;
    background-color: lightblue;
    border: 1px solid black;
}

#DIV2 {
    position: relative;
    top: 130px;
    left: 30px;
    width: 300px;
    height: 150px;
    background-color: coral;
    border: 1px solid black;
}
</style>
</head>
<body>

<p>Click the "Try it" button to change the z-index of the blue DIV element:</p>

<button onclick="myFunction()">Try it</button>

<div id="DIV2">
  <h1>Voila!</h1>
</div>

<div id="myDIV">
</div>

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

</body>
</html>