Coming from recent patch on modern Vector to set media queries to being em based, we should consider exemplify the ideation and thoughts behind.
The original article by Zell from 2016 on comparing em, rem and px: https://zellwk.com/blog/media-query-units/
And 2015 article on why em media queries are root font-size independent: http://blog.w3conversions.com/2015/03/all-your-base-are-belong-to-us-%E2%80%94-or-what-base-size-do-em-based-media-queries-use/
StackOverflow article on clarifying the em root independence stated in the specs: https://stackoverflow.com/a/29723215/1696030
Proposal is to expand the sizing units section by a paragraph accordingly.