So I was actually just about to write a cross-platform app using https://material-ui.com/ https://material-ui.com/ purely because it is the most comprehensively

So I was actually just about to write a cross-platform app using https://material-ui.com/ https://material-ui.com/ purely because it is the most comprehensively fully developed and React-first toolkit for React out there. Plus it has 11k (edit: oh it's 37k, wow) stars on Github, more than twice as much as the next most starred React toolkit. Semantic and Bootstrap have been "ported" to React and are missing features or do things non-idiomatically, whereas MUI was built with React in mind (twice if you count the rewrite). There are other React-first toolkits but none are nearly as comprehensive and "healthy". But I've been on the fence because it feels really weird to write a cross-platform app (mobile and desktop) using components that are clearly designed to look like just one platform (Android). Technically I could make a custom theme for it, but that looks extremely complex, and OP's linked theme is practically the only free one I could find. I'd love to just abandon toolkits like this and write my own React components specific to my app, but honestly I don't know how to make half the stuff that's in these toolkits. My JS/CSS is just not that strong.