I am struggling to use themes consistently (which unnecessarily breaks my workflow) as most of the ones I am using completely ignore what I have in Interface Font, Text Font, and Monospace Font. Is there anyway to force any theme to accept the fonts we provides in Appearance w/o modifying the CSS file? Otherwise, what’s the point of these options when any theme can come along and completely ignore the settings that you actually want. Won’t specify specific themes (unless asked) since it’s common among most of them.
Themes are just CSS and written by community members volunteering their time; they are gifts.
The font settings in Appearance are relatively recent, added only in the last year. Some of the themes use the Style settings plugin to adjust fonts (also pre-dates the font settings in appearance). Not all of the existing themes have been updated to use the new font settings and will be updated when their authors have time.
There isn’t any generic way to force all themes to use the new settings as each theme is constructed differently.
If you have the skills to use css, git, and github, you might consider creating a pull request to update the themes you care about. Or you can explore other themes.