>"Or whatever" wasn't intended to denigrate Bootstrap but to head off any instruction that there are other options. Certainly when I mention bootstrap to bright young things, invariably one of them opines "oh don't use bootstrap, use " ... and sings the praises of some amazing new Rube Goldberg option that derails the point we're discussing. Probably less of a risk here, but it' a habit now.

These days bootstrap is considered 'old school' and stodgy - it's like the new Battleship Gray office design... but as all things that depends on how you actually use it. I've used a lot of different UI frameworks including Material Design (what cluster that is), Foundation (Ok) and a few really esoteric ones. I always find myself going back to Bootstrap as my preferred framework, because it's highly functional out of the box and maybe more importantly very adaptable to custom CSS. The bar of entry for custom modifications is low, which is also why there are many more bootstrap styled components than any other frameworks.

But I think the overall point is that one way or another one has to choose a framework of some sort because it's simply to complex to roll your own anymore. Standard HTML controls just don't cut it (it's maddening) as browsers all render them differently. So CSS Framework are more of a tool to force basic consistency on a design. If you use any framework you have to follow some rules and that's generally a good thing for consistency. It doesn't matter which one but a framework is definitely required for just about any HTML based app.

When comparing native Mobile to HTML the big thing you'll find is that UI design of all the things is a bear, especially if you expect to have things behave in a 'forms based' manner. Looking at an iOS designer canvas for the first time is like looking at a map written in Russian :-). It's funny to think that the concepts of something so simple can be so different. Using native designers also forces you into a framework, but it's considerably harder to customize native controls than it is to customize or build custom HTML controls. Usually the only effective way is either to have hotshot designer on your team, or you buy third party control suites. Considerably less flexibility. The bar of entry is a lot higher with native IMHO, and while I think for consumer facing applications an App may be a requirement, for business facing applications I think it's questionable that the overhead of creating and publishing native apps provides additional value over an HTML based application. You can certainly build a nicer more responsive UI with native but it takes a lot more effort and skill to do so...