You can edit / change the code and click run button <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>Marked text Tag</title> <script>var clicky_site_ids = clicky_site_ids || []; clicky_site_ids.push(101319977);</script><script async src="//static.getclicky.com/js"></script> <h2>HTML <mark style="background-color:red;">Marked</mark> Formatting</h2>