Thirds post property specifies the size of the background images

The background-size property specifies the size of the background images.

There are four different syntaxes you can use with this property: the keyword syntax (“auto”, “cover” and “contain”), the one-value syntax (sets the width of the image (height becomes “auto”), the two-value syntax (first value: width of the image, second value: height), and the multiple background syntax (separated with comma).