I miss the times before applications had their own theming and just used bog-standard OS provided widgets that could be themed globally by the user. That this has fallen out of favor is, in my opinion, a good indication of how unprofessional and user-hostile our industry has become.

We didn't use to need bespoke "dark modes", you just changed the colors globally. We did this in the 90s, when 64MB of ram was huge. We have become pathetic.