Throughout MediaWiki core and extensions we have a unbearable mess mish-mash of em, px (and furthermore %, pt (for screen CSS!) and newest addition rem/vh values).
We should reconsider especially the first two in where to use what to serve whom.
Some questions in the year 2018; relying on px only would simplify a few things on the programming side. So let's evaluate possible issues:
- Does it make sense to rely on ems for font-sizes and distance/positioning values?
- Text zooming got completely(?) out of fashion, support is somewhere hidden in submenus in remaining implementations (Firefox > Zoom > Zoom Text only), IE 6-8 should not be a show stopper for us any more
- Do we need a combination of both, but allowing ems only for font sizing, line height (with help of stylelint)?
- Are there other technical restrictions to consider moving away from em only?
- any mobile browser with considerable market share,
- assistive technology building on top of font size based zooming, although not related, similar things like T204807 comes to my mind