Adding Banner to GitLab UI

GitLab CE
I am trying to add a Banner to the top of the page in the GitLab UI,
I modified the /assets/application.css to include a ::before css rule.
This works great in older version of firefox, but newer versions firefox and chrome do no pick up the new .css file. I place a new file (with a different name) in the assets directory and pulled the file down in the browser fine. But when I try to pull down the modified application.css file. I get the original version, without my ::before rule.