This is almost per-pixel identical to the resume layout that I used to have laid out in a normal editor exclusively for PDF and print, but without making a single concession with my normal print layout, it also seamlessly collapses into single columns perfectly fine on mobile devices, doesn't require Javascript, and the entire layout is ~160 lines of CSS.
And to be clear, this is bad CSS. This is not CSS I'm proud of, this is CSS I wrote ages ago that I'm going to be tackling very differently whenever I get around to rewriting the resume. But it's still perfectly reasonable to have document layouts that feel like normal print layouts that collapse down well on mobile devices.
And sure, this is a trivial example, but I think the same principles scale up. I don't believe that applications are different. Most application UIs can be represented as trees, and trees are well-suited for multiple-column layouts and collapsing rules based on width. That many sites work on mobile and don't scale up is a result of developers designing primarily for small screens and not thinking about large screens at all.
Even here, this resume should handle wider screens better, it doesn't take enough advantage of available width. But the other thing about the web compared to native is that with native toolkits if a developer designs for mobile and then doesn't think about desktop, the app just doesn't work on desktop at all and you can't use it.
On the web, if a developer designs for mobile and doesn't think about desktop, at least the interface is still usable on desktop. And vice-versa: there are desktop interfaces on the web that are miserable on mobile devices. But they work. None of the alternatives that people are proposing have that advantage.
