For me personally, the challenge UI frameworks like Bootstrap solve is the pure UI. That is, which borders, shadows and spacings to use and such stuff. A thin l

For me personally, the challenge UI frameworks like Bootstrap solve is the pure UI. That is, which borders, shadows and spacings to use and such stuff. A thin layer on top of the actual APIs like Mozilla Brick does not seem too useful to me - why bother adding a third party component if it merely wraps the functionality of HTML/CSS? (Although I must admit I haven't used Brick yet.)