Fixes#10580
Remove obsolete styles so that people do not trip over them.
I went through the codebase with `rg` and made sure that the only elements which had potential to use such mix of classes were doing so accidentally, and removed all the unused code.
### A small fix for Forgejo themes
Ref https://codeberg.org/forgejo/forgejo/pulls/10581#issuecomment-9245399. The missing variable was used in one place outside of devtest.
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/10581
Reviewed-by: Michael Kriese <michael.kriese@gmx.de>
Reviewed-by: Beowulf <beowulf@beocode.eu>
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: 0ko <0ko@noreply.codeberg.org>
Co-committed-by: 0ko <0ko@noreply.codeberg.org>
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