Background Size

The background-size property controls the size of the background image.

Value	Description
auto	The background image is actual size (default).
cover	Set the background image to cover the element's entire area. The image retains it's proportions and so is cropped if necessary.
contain	Scale the image to the largest size such that both its width and its height can fit inside the content area.
numeric	Specify two values separated by a space. The first is the width, the second is the height. px and ems etc can be used for the units. If you specify percentage units, this is calculated based on the width/height of the element.