Background Size

• The background-size property enables one to control the scaling of the background-image.

• It takes up to two values, which determine the scale/size of the resulting image in vertical and and horizontal direction.

• If the property is missing, its deemed auto in both width and height.

• auto will keep the image's aspect ratio, if it can be determined. The height is optional and can be considered

Therefore, on a 256 px × 256 px image, all the following
auto.

• background-size settings would yield an image with height and width of 50 px:

 background-size: 50px;
 background-size: 50px auto; /* same as above */
 background-size: auto 50px;
 background-size: 50px 50px;

• Reference: 5.5