Using app-specified custom CSS

[Meddysong]

I was about to create a new custom CSS file when I noticed it's possible to create an app-specific one which, I imagine, will only run when the page being loaded is a particular app:

 

And there it is, complete with a couple of bits of CSS just to test it:

But once I go to Downloads, nothing has changed. And when I look at the source code, I find that there isn't a separate custom file created from this CSS file, and nor has it been compiled within the normal custom.css file.

Am I using it as intended and it's just not working? If not, how is this feature of creating app-specific CSS files in the ACP supposed to work?

 

[SJ77]

I have the same question right now