I think NYTimes.com is a good example. Theres a hamburger menu that expands to the whole screen when on mobile or tablet; its a sidebar on desktop. The whole arrangement of articles becomes linear on mobile; it isnt on desktop. It looks like someone figured out how it should look at every state, and then developed a way to gracefully switch between them -- not that it was a mobile UI that someone decided to enlarge on desktop.

This is why we have media queries in CSS!