Consider an above/below layout mode

[ferdnyc]

For narrower screens, particularly mobile devices, the side-by-side layout of the editor may leave both the source code area and the render canvas feeling a bit squashed horizontally,when they'd fit quite comfortably in an above/below arrangement.

Consider either having the layout automatically flip to above/below when the screen width is below a certain threshold, or adding an option to the settings to flip the layout.

(For extra credit, the interface could go full Compiler Explorer, with draggable sections that can be repositioned at will — Matt Godbolt uses golden-layout for that — but that's a lot more work than a simple responsive arrangement.)