So today I received a job where I needed to match a websites responsive header to one of the games the company I am working for is making. Simple enough really. When I started to look at the source code I could see that the developer was using EM rather then PX for their break points. After quite a lot of searching around the internet I couldn't see why using that unit of measurement in a media query was "better" than using px. Any one care to enlighten me?