<!DOCTYPE html>
<html>
<body>
<p>This is a p element.</p>
<p>This is also a p element.</p>
<p>Click the button to add a background color to the first p element (index 0) in the document.</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");
x[0].style.backgroundColor = "red";
}
</script>
</body>
</html>