Lighter

Micro CSS library A set of small, responsive CSS modules that you can use in every web project.
Unlike other frameworks, Pure's design is unopinionated, minimal and flat

Lighter is Extremely small. The entire set of modules clocks in at 4.1KB* minified and gzipped. Crafted with mobile devices in mind, it was important to us to keep our file sizes small, and every line of CSS was carefully considered. If you decide to only use a subset of these modules, you'll save even more bytes.
github link here