Margin padding của bootstrap

Bootstrap có quy định
- container, col : padding: 0 15px;
- row: margin : 0 -15px;
Như vậy xem hình như sau:

How to make items to div center in css. (vertical-align)

First you mush set type of his parent to : POSITION: RELATIVE
Then, you set type of them to : POSITION : ABSOLUTE 
Now, you set it :
TOP: 50%;
LEFT: 50%;
TRANSLATE(-50%,-50%)

It will go to center of div. thanks all to watch my topic about "How to make items to div center in css. (vertical-align)"