Styletron is an universal toolkit for component-oriented styling. It falls into the CSS in JS category. Styletron works great with React but can be used with other frameworks or plain JS as well.

Near-zero runtime, server-side rendering, multi-variant support, and a best-in-class developer experience.

Fela is a small, high-performant and framework-agnostic toolbelt to handle state-driven styling in JavaScript.

Styled System lets you quickly build custom UI components with constraint-based style props based on scales defined in your theme.