<!DOCTYPE html>
<html>
<head>
<style>
#myDIV {
border: 1px solid black;
margin: 5px;
}
</style>
</head>
<body>
<div id="myDIV">
<h2 class="example">A heading with class="example" in div</h2>
<p class="example">A paragraph with class="example" in div.</p>
</div>
<p>Click the button to add a background color to the first element in DIV with class="example" (index 0).</p>
<button onclick="myFunction()">Try it</button>
<p><strong>Note:</strong> The querySelectorAll() method is not supported in Internet Explorer 8 and earlier versions.</p>
<script>
function myFunction() {
var x = document.getElementById("myDIV").querySelectorAll(".example");
x[0].style.backgroundColor = "red";
}
</script>
</body>
</html>