Page 66 - CSS

contain

contain

Scale the image, while preserving its intrinsic aspect ratio (if any), to the largest size
such that both its width and its height can fit inside the background positioning area.

This makes sure that the background image is always completely contained in the background
positioning area, however, there could be some empty space filled with your background-color in
this case:

cover

cover

Scale the image, while preserving its intrinsic aspect ratio (if any), to the smallest size
such that both its width and its height can completely cover the background positioning
area.

This makes sure that the background image is covering everything. There will be no visible
background-color, however depending on the screen's ratio a great part of your image could be cut
off:

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