You can edit / change the code and click run button
<!DOCTYPE html> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/> <script src="../../../ajax/libs/jquery/1-11-3/jquery.min.js"></script> <script> $(document).ready(function(){ $("button").click(function(){ $("p:first").addClass("intro"); }); }); </script> <style> .intro { font-size: 150%; color:green; } </style> <script>var clicky_site_ids = clicky_site_ids || []; clicky_site_ids.push(101319977);</script><script async src="//static.getclicky.com/js"></script></head> <body> <h1>When you click the button, it will add myclass styles to the paragraph</h1> <p>This is a paragraph.</p> <p>This is another paragraph.</p> <button>Add a class name to the first p element</button> </body> </html>