<!DOCTYPE html>
<html lang="en-US">
<body>
<h1>CSS font-size Property</h1>
<button onclick="myFunction()">Click Me</button>
<script>
var x = document.getElementsByTagName("h1")[0];
function myFunction(){
x.style.fontSize = "40px";
}
</script>
<p><strong>Note</strong>: click on the button to change the font-size.</p> </body>
</html>