File titles overlapping diff summary in branch compare when scrolling

Summary

Super minor, but in the branch compare section, file-title-flex-parent divs overlap over the diff-files-changed div (first having a z-index of 220 and latter having 200)

Steps to reproduce

Have enough changes on a branch that you can just scroll down and have the title of one of the files overlap.

Example Project

Using a private repo, so I can't right now (at work), but I'll do it later if it's really necessary.

What is the current bug behavior?

File titles scroll over diff summary bar when scrolling.

What is the expected correct behavior?

Summary bar should probably be on top at all times.

Relevant logs and/or screenshots

Output of checks

This bug happens on GitLab.com

Possible fixes

file-title-flex-parent has a z-index of 220 (I can't find where it comes from though. everything seems to point at it having 120...) whereas diff-files-changed has 200. Haven't checked what the repercussions of changing either of these would be, but that seems like the logical solution.