The margin property sets the amount of padding from each edge of an element.
Padding is the space from the border of the current element to the inner border of its parent element.
If the element has no parent, the padding will be the distance from the edge of the element to the edge of the browser window, given that the window itself also has padding set by default. To get rid of them, you should set the margin value for the body selector to zero.
The margin property allows you to set the amount of indentation for all sides of the element at once, or to define it only for the specified sides.
margin: [ length | percentage | auto ]{1,4};