[fuzionmonkey]

One thing worth mentioning about class composition with CSS Modules is it allows for the convenient ergonomics of Sass's @extend without any of its problems.

Sass @extend is actually counterproductive in terms of reducing filesize [1] and results in unwieldy, unreadable CSS rules [2]. In contrast, CSS Modules achieves true class reusability and optimal de-duplication of styles in a manner impossible with Sass, resulting in a nice Chrome Inspector view because the original classes are preserved and their composition is naturally represented.

[1] https://tech.bellycard.com/blog/sass-mixins-vs-extends-the-d...

[2] http://pressupinc.com/blog/2014/11/dont-overextend-yourself-...