Create an option to toggle rules for Web IDE
The Web IDE seems to have a complete dark theme implemented, which is applied if "Dark" is selected as the "Syntax highlighting theme" in the account preferences. So, using this preference makes the rules defined by the userstyle specific to that page redundant.
For this reason, it would probably be a good idea to add a switch in the style options that allows the user to disable all rules specific to that page, and also mention that in the README.