File tree/header looks a little odd when scrolled

[njx]

1. Open a project with a lot of files (or expand a lot of subfolders)
2. Scroll down in the file tree so that the top of one of the filenames is clipped

Result: Looks a little odd when it's clipped, because there's no visible affordance underneath the "Project Files" header that's clipping it. One solution I saw recently that I liked is in Gmail: when you scroll the content, a shadow appears underneath the header area. Seems simple to implement.

[njx]

I'm going to close this out since we're going to be implementing a new visual design at some point anyway.