Board Thread:General Discussion/@comment-38626034-20190831035843/@comment-9605025-20190831151211

You can only do this for wikis on which you are an admin. The reason is it requires you to modify the site's CSS. There is no way for you to do this accross all wikis. If you are looking to do this for particular wikis on which you are an admin, then NightSpeakers has already given you what you need to start.