Question

I’m guessing that because you can do this with Media Queries:

@media (min-width:500px) { … }

That at some point or another, the CSS stylesheet must know what width the screen is, sans Javascript.

Is this the case?

Answer 1

You can use device-width which will test of the screen’s width in px. That however is not entirely recommended. Use max-width and min-width (for the viewport) instead.

---

If you are trying to GET the screen width and use it (something like content: (device-width); of some sort, that’s not possible. Stick with JavaScript.

Manual Reference