Defines the position of the background.
| Center | Vertical alignment is centered and/or Horizontal alignment is centered. This is the default value to make sure it's backward compatible with unity-background-scale-mode default value. |
| Top | Vertical alignment is at the top. |
| Bottom | Vertical alignment is at the bottom. |
| Left | Horizontal alignment is to the left. |
| Right | Horizontal alignment is to the right. |