Userstyles only work client-side and generally per-site (I use userstyles and created some).
If someone would like to suggest improvements to the overall appearance of Discourse, any suggestion can be made in ux, and if nobody creates a theme component or include wanted changes in Discourse, any user can make his own solution I guess. Whether it’s a theme component if they’re admin or a client-side solution if they’re not, with their own CSS from whatever browser plugin floats their boat.
But then, this is not really a Discourse-oriented discussion anymore I guess.
@GVG take a look at this related discussion, it could be interesting to you: