from Css backgrounds and borders module level 3. The image can be left to its natural size, stretched, or constrained to fit the available space. Lengths, a width and a height, such as 100px 50px (100px wide, 50px high). You can use any css size units you like, including pixels. Prefix to any existing background size utility. Css backgrounds and borders module level 3. The background image will retain its original size.
Auto sets the background image in its original size. You can control which variants are generated for the background size utilities by modifying the backgroundsize property in the variants section of your.