[creichenbach]

Well, to have a perfect-ish solution, you'd have to build a framework with UI elements that map to native elements on each platform. Behavior and styling (e.g. positioning of elements) would need to be consistent, so you'd probably have to reduce functionality to the least common denominator for each possible dimension, or take the burden of implementing compatibility for A on platforms B and C. Web has a legacy of document-based components, while mobile is generally more interactive. There are overlaps nowadays, but staying within those boundaries would be a serious restriction.

On top of all that, you'd need a runtime that works on all platforms and is able to interact with native controls. I think React Native does something like that, but back then when I checked they did not have official web platform support (which is somewhat ironic, but I suspect technical difficulties too).

[aatd86]

Oh ok. So that's layouting that is different? (all else being accounted for)

[creichenbach]

Well, among other things. Native APIs are another thing that comes to mind, but those can be bridged more easily I suppose.