Add a fixed top bar or a back to top icon

## Feature Request

**Is your feature request related to a problem or unsupported use case? Please describe.**
When my doc is super long I need to scroll all the way up to get acess to the sharing / download and ... menu.

**Describe the solution you'd like**
I'd like the top bar to be fixed or have back to top button

**Describe alternatives you've considered**
Scroll back up ...
