So I used PicoCSS as the foundation of µCSS, adding: a 12-column responsive grid (5 breakpoints), 17 UI components (accordion, modal, toast, tabs, nav, breadcrumb...), 20 color themes, and utility classes for color and positioning. Dark mode is built in, automatic or manual.
At ~19KB gzipped, it's significantly smaller than Bootstrap (~30KB), and it requires no JavaScript to work — CSS only.
Each theme is a single self-contained CSS file, ready to drop in via CDN.
GitHub: https://github.com/Digicreon/muCSS
Happy to discuss the design decisions.