Visiting any page on a mobile site that has custom styles defined in MediaWiki:Mobile.css, I noticed that if I disable JavaScript, the stylesheet of MediaWiki:Mobile.css is not loaded.
For example:
https://es.wikipedia.org/wiki/MediaWiki:Mobile.css - It contains CSS to force the display of references in one column on mobile devices
https://es.m.wikipedia.org/wiki/Abraham_Olano#Referencias - If you disable JavaScript in your browser, references are displayed in 2 columns. If you enable them, references are displayed in one column.