what is base for em value in margin's and padding's element?

[oranoos3000]

hi
1-what is base for em value in margin's and padding's element?
do width of the containing block is base or these are calculated the same percentage value for this propery?

2-how does interpret negative margin for an element that cause overlap that element with other element?

thanks alot for your help.

[Dormilich]

check the wikipedia article for what em means and also the external links that explains em in CSS context.

to summarise it: em is a relative unit that per se does not have a fixed value, but rather is calculated from the fixed default settings in your browser/CSS.