Feature request: dark mode

First of all, thanks for this framework! 

Dark mode is pretty popular these days and would be a nice addition.

It seems like Bulma does not have native dark mode support yet: https://github.com/jgthms/bulma/issues/2342

There is an extension for it (https://github.com/jloh/bulma-prefers-dark) although I'm not sure how well that would work with this framework.

Thanks again!