Theme development: Path to external resources

[shahroq]

I see in new themes like Atomic, as default, the main CSS file is generated by webpack/mix and located in the theme folder (/concrete/themes/atomik/css/skins/default.css). However, when site editors use the core customizer feature and create a new skin, the outputted CSS file is generated by Concrete and saved in a different place (/application/files/presets/atomictest1.css).

So in a situation where there is reference to the external file like image/font/etc, how does the pathing work? I see in the former situation, webpack/mix could handle it. But what about the second scenario? Is there an environment variable that can be added as a prefix to paths in SASS files? Or any other approach for this matter? I wonder if this has been thought of and there is already a solution that works in both scenarios.