Add a "Back to Top" button or static header to Pull Request review pages. (customer request)

If you spend a lot of time in lengthy pull requests, scrolling down and reviewing code, only to have to scroll all the way back up to the top in order to merge or decline the request.

Would it be possible to either add a "back to top" button somewhere as you scroll down, or make the "merge, decline etc" header static as you scroll down so it is always visible.

It's a small change but would make a big difference to us when reviewing code.