If you don't mind, I have a some followup questions that might help us figure out what's going on...
- Does every user of your Canvas instance have this same issue, or just you?
- What browser/operating system are you using? Have you tried another device or browser (if possible)?
- Do you know if your Canvas instance is hosted by Instructure? Since you have Canvas Studio, I assume it is, but always safer to ask.
- Are you a Canvas admin, a teacher, or do you have some other role?
If it's not your custom css, let us know the answers to the questions asked and we can probably give some further troubleshooting tips.