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Twitter post by Daniel Feldman (@d_feldman): Linux is the only major operating system to support diagonal mode (credit [Twitter] @xssfox). Image shows an untrawide monitor rotated about 45 degrees, with a horizontal IDE window taking up a bottom triangle. A web browser and settings menu above it are organized creating a window shape almost like a stepped pyramid.
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That just means it shouldn't be a native app or a web app, but instead should be a plain ol' webpage that doesn't try to do app-y things in the first place. The notion that web pages have any legitimate reason to know your viewport size (let alone anything at all about the screen hardware itself) is like one of those "statements dreamed up by the utterly deranged" memes, except not satirical.
Seriously: literally the entire defining principle of HTML (well, aside from the concept of "hyperlinks") is that the client has the freedom to decide how the page should be rendered, but misguided -- or megalomaniacal -- ~~graphic designers~~ ~~webmasters~~ front-end web "devs" have been trying to break it ever since.
Lol - in your other comment you suggested that web devs key off of screen rotation to resize the page, but now you're saying the client shouldn't know anything about the viewport at all? Which is it? And why would the rotation angle be useful if I don't know the aspect ratio of the screen? Or are we now assuming that widescreen will be a thing forever? I thought your ingenius idea was to be able to handle any use case.
Legitimate apps key off screen rotation do fancy stuff. Web pages let the browser render them and don't try to do fancy stuff. It's not that fucking hard.