I can't get the CSS from the Labels Menu

Bug Reports
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#1

Description

When I open the inspector and try to get the CSS classes from the Labels menu that are on a popover div, content is removed from body. I can’t finish my theme!

To Reproduce…

Steps to reproduce the behavior:

  1. Open inspector
  2. Click the labels menu
  3. try to see the content of mailpopover to get the CSS
  4. content is gone as menu is removed from dom tree.

Expected Behavior

Where is the CSS documentation?!

Additional Context

I just want to finish my pitch black DarkKnight theme that you can see here:

Obs: I know the .less file could be better, I just want it to work.

(Originally posted by phackwer on GitHub.)