If you are looking for a UI framework, checkout IBM Carbon: https://carbondesignsystem.com
I used it to build a merge conflict tool: https://codeinput.com and while it required a much deeper understanding than just reading the docs (tons of bugs), it is by far the most comprehensive UI framework out there. Most UIs either lack lots of components or are made by a couple front-end/react/css guys. This inevitably means that they lack research into things like typography, accessibility, patterns, etc..