Split styles (mobile, desktop)?

Question

css

Good afternoon. Has anyone encountered splitting existing styles into mobile and desktop versions?
In general, there is a main.css file, it contains all styles, responsive (not mobile first). You need to make 2 files mobile.css and desktop.css out of it, so that in the mobile.css file there are styles only for mobile, and in the desktop there are styles only for the desktop. I was looking for plugins on postcss, that's not all. Or is it still not steamed and done by hand?

Answer 1

bootstrap?