<!DOCTYPE html>
<html>
<head>
<script src="/lib/jquery-1.12.2.min.js"></script>
<script>
$(document).ready(function(){
$("button").click(function(){
$("p").toggleClass("main");
});
});
</script>
<style>
.main {
font-size: 120%;
color: red;
}
</style>
</head>
<body>
<button>Toggle class "main" for p elements</button>
<p>This is a paragraph.</p>
<p>This is another paragraph.</p>
<p><b>Note:</b> Click the button more than once to see the toggle effect.</p>
</body>
</html>