Comment by BrenBarn

I'd go even more basic than this: only use native everything. It's a travesty that web pages are to use use custom controls or have any kind of look and feel different from the native OS ones. The look and feel of everything (every app, every webpage) should be determined by the end user, via their OS settings, not by the author of the app or document. What we have is designers being able to get to "my app/webpage looks the same for everyone"; what we ought to have is users being able to get to "every app/webpage looks the same for me".