Relative to the font-size of the parent element (2em means 2 times the size of the parent font-size). We should be careful when we use

em

because if we have 3 containers nested inside of each other with

2em

, then the child element will have 8 times more font-size than it's grand parent container (it means they cascade)

https://www.w3schools.com/cssref/tryit.asp?filename=trycss_unit_em

https://youtu.be/-GR52czEd-0?t=279