<!DOCTYPE html>
<html lang="en-US">
<head>
<style>
.one{
color:red;
}
</style>
</head>
<body>
<p>Click on the button to toggle the "one" class to this paragraph.</p>
<button onclick="myFunction()">Toggle Button</button>
<script>
var elem = document.getElementsByTagName("p")[0];
function myFunction(){
elem.classList.toggle("one");
}
</script> </body>
</html>