enquire.js : A lightweight, pure JavaScript library for responding to CSS media queries.
css3-mediaqueries-js : make CSS3 Media Queries work in all browsers (JavaScript library)
voxel.css : The goal of this project is to provide a lightweight 3D CSS library with very simple implementation.
darken : Easy control over your dark mode in a web environment
Photon : UI toolkit for building desktop apps with Electron.
A modern, HTML5-ready alternative to CSS resets
Normalize.css makes browsers render all elements more consistently and in line with modern standards. It precisely targets only the styles that need normalizing.