We currently have to scroll all the way to the top if we want to be navigated to a
specific diff file.

I added a floating banner to the diff view that sticks to the top of the page when
the user has scrolled down on the page. On this banner, I will further add a
collapsed list of the diff files, showing only the the file that the user is currently
looking at. The user will be able to expand this list to navigate to the other files.

The banner is currently invisible when the user has scrolled down on the page.
The floating banner is currently only operating in the background.

Used the chrome web dev tools to make sure the banner has been

added the the DOM. While scrolling on the diff page, I could 

see that the styling and width/margin values were changing, 

which tells me that the banner is responsive and the 

functionality is working.