Tryit Editor v2.7

Edit This Code:
<!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 in the document.</p>

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

<script>
function myFunction() {
    document.querySelector("p").style.backgroundColor = "red";
}
</script>

</body>
</html>