So what is EM?

So your wondering what EM is, well firstly to sum it to a basic form its a type of CSS sizing for text. In a more detailed explaination EM is a type of sizing for text that is measured using the size of M in the parentfont size, for example if a page body was set to font-size: large, 1 em would be equal to that size.

EM is mainly used to cross between browsers, it has better compatibility for when size is changed in a new browser the text size scales. For example if one site is set to default font-size small and one set to large, the EM will scale to this.