The Wix dev team throws their hat into the CSS preprocessor ring:
Stylable is a CSS preprocessor that enables you to write reusable, highly-performant, styled components. Each component exposes a style API that maps its internal parts so you can reuse components across teams without sacrificing stylability.

Scopes styles to components so they don’t “leak” and clash with other styles.
Enables custom pseudo-classes and pseudo-elements that abstract the internal structure of a component. These can then be styled externally.

Styleable is a post from CSS-Tricks