As of inkscape 1.4, the default themes are general GTK themes (Adwaita or Minwaita), which should work OK in theory, but in practice they still result in various parts of Inkscape's UI having uneven spacings, "weird" margins, and other UI inconsistencies. This is because unless the application makes a dedicated effort to honour a theme's spacings, it can be very easy to drift out of the theme's intended look.
This project is an effort to maintain a dedicated stylesheet for the latest of each of Inkscape's major releases.
Sounds good. I'll check it out some time. Thanks for taking the time.