When it comes to supporting multiple devices, I try to design UI with smaller screens in mind first (in terms of physical size, not resolution. 1920x1080 is a fine base resolution.) Scaling a compact, minimal UI up to desktop size is easier than having to squish a complex scene down onto a phone screen. You want to make sure players can see everything in your game clearly, even on the smallest screen size you plan to support.
There's a button in the DevTools panel on Google Chrome that lets you see how a page looks on different devices. That might help you judge how big to make the room.
Also, since it's a pixel art game, make sure you scale the graphics independently of the screen resolution, or else things will appear smaller on high-dpi screens. How you do this depends on the engine you're using.