Anyone can explain this sentence in this website explaining units?

Question

In this website, in the subheadline which is at the middle of the page, "What about medai quaries" then "here are some example" then example 1 and 1b, the sentence is "So we can't use 6dp for Ems because it hits both media enquiries." Why?We need a unit that hit in both situation right?
https://engageinteractive.co.uk/blog/em-vs-rem-vs-px

Answer 1

Media query should be detailed and specified on different screen size like a ladder. If both media enquiries matched, the styling in latter one will override the styling in former one.

em is based on the base font size set on body.

Better explanation can be found in these three Q&A

https://www.sololearn.com/discuss/1646442/?ref=app
https://www.sololearn.com/discuss/1650909/?ref=app
https://www.sololearn.com/discuss/1651668/?ref=app

Answer 2

Thank you so much!