Documentation:
Image Box

Here you control how the image looks within the image box. There are separate settings for desktop, tablet, and phone.

Repeat

Here you can choose to repeat the image within the image box.

Note: This effect will only be visible if the size of the image is smaller than the image box.

Size

Here you can set a custom size for the image. The percentage value represents the image width as a proportion of the image box width.

Example: 100% will make the image the same width as the image box, while 50% will make the image half the width of the image box.

See here for more details.

See here for an example.