<!DOCTYPE html>
<html>
<body>
<h2 class="example">A heading with class="example"</h2>
<p class="example">A paragraph with class="example".</p>
<p class="example">Another paragraph with class="example".</p>
<p>Click the button to add a background color to the first p element (index 0) in the document with class="example".</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.querySelectorAll("p.example");
x[0].style.backgroundColor = "red";
}
</script>
</body>
</html>