Fix Slack.com  (#7987)
Fix Slack.com  (#7987)

  - The invert logo on the homepage no longer works (the logo is now an SVG, and has a newly named class)
  - Buttons in the actual "app" aren't darkened properly

Co-authored-by: Gusted <d02dbed052e28c2380acdd37568fd76142823678@hotmail.com>
alexanderby/darkreader,alexanderby/darkreader,darkreader/darkreader,darkreader/darkreader,darkreader/darkreader,alexanderby/darkreader