Sticky diff file headers do not show on compare page

Summary

On medium screens on the the "Compare" page, the sticky diff file headers get covered up because the header takes up more than one line.

Steps to reproduce

Click on repository, compare, and select two versions with more than a page length of diffs and scroll down till theres a sticky header. Then reduce the window width to about 900px and observe you can no longer see the file headers.

What is the current bug behavior?

Sticky file headers are not visible

What is the expected correct behavior?

Sticky file headers should be visible

Relevant logs and/or screenshots

Possible fixes

Two possible solutions come to mind:

1. Push the file headers down when the sticky header takes up two lines (Likely requires some messy javascript with a window resize listeners)
2. Make sure the header won't wrap lines onto the next line