CSS margin,padding percent

The percentage of margin,padding is calculated relative to the width of the nearest parent container.

<! DOCTYPE html>
 
 
The main reason for guessing:
 
1, in order to unify the ratio, if the width and height of the same (for example, are all 10%), the result of the page results show a 100px, a 200px so big, it is too bad;
 
2, page layout habits. We are accustomed to sliding the page up and down, not accustomed to sliding around, so the page is usually designed to be around just covered, drag up and down, height is not fixed. This is easier to control with the width of the reference.