<html xmlns="http://www.w3.org/1999/xhtml"> <head> <style><![CDATA[ .green { color: green; } .toremove { color: red !important; } ]]></style> </head> <body> <div class="foo toremove"> This should be green </div> <script> var div = document.getElementsByTagName("div")[0]; div.classList.toggle("toremove"); div.classList.toggle("green"); </script> </body> </html>