Tryit Editor v1.8

Source Code:

<!DOCTYPE html>
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js">
</script>
<script>
$(document).ready(function(){
  $("#add").click(function(){
    $("p").toggleClass("main",true);
  });
  $("#remove").click(function(){
    $("p").toggleClass("main",false);
  });
});
</script>
<style type="text/css">
.main
{
font-size:120%;
color:red;
}
</style>
</head>
<body>

<p>This is a paragraph.</p>
<p class="main">This is another paragraph.</p>

<button id="add">Add class "main"</button>
<button id="remove">Remove class "main"</button>

</body>
</html>

Result:

W3Schools.com - Try it yourself

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