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CSS CSS Basics Understanding Values and Units Em and Rem Units

Posted by Peter Huang
Peter Huang
5,427 Points

I understand the difference between Em and Rem for CSS, but Rem seems easier than getting confused by Em and changing al

I understand the difference between Em and Rem for CSS, but Rem seems easier than getting confused by Em and changing all over and getting confused..

What is the advantage of using Em and stress with the calculation? Is it because different screen have different font size and Em will be able to show layout exactly in all font size and calculate it? I dont get why people stress using em..

1 Answer

Steven Parker
Steven Parker
231,268 Points
Steven Parker
Steven Parker
231,268 Points

The value of em is that it is relative to the font size of the parent element. So if you want an element to differ from it's parent by a certain percentage increase (or decrease) in font size, using em allows that relative change to be preserved if future changes are made to the parent element.

On the other hand, rem keeps the target element font size the same if and when a change is made to the parent element. So it's basically a design decision — are you choosing a specific size for the element based only on the root document font size, or are you creating a percentage change relative to the parent element?

Peter Huang
Peter Huang
5,427 Points

thanks so much. this makes a lot of sense.