<!DOCTYPE html>
<html>
<head>
<style>
#myDIV {
border: 1px solid black;
margin: 5px;
}
</style>
</head>
<body>
<div id="myDIV">
<h3>A h3 element in div.</h3>
<p>P element in div.</p>
<span>A span element in div.</span>
<h2>A h2 element in div.</h2>
<div>A div element in div.</div>
<p>Another p element in div.</p>
</div>
<p>Click the button to add a background color to the fourth element inside the div element.</p>
<button onclick="myFunction()">Try it</button>
<script>
function myFunction() {
var x = document.getElementById("myDIV");
x.getElementsByTagName("*")[3].style.backgroundColor = "red";
}
</script>
</body>
</html>