It must be CSS in the end, but you should create/use a component library, that has the right set of primitives (and less-primitives) that lets end feature devel

It must be CSS in the end, but you should create/use a component library, that has the right set of primitives (and less-primitives) that lets end feature developers create the UIs without having to resort to manually write CSS. THis is made significantly easier when you have designers working with this "design library" mindset also.