A linear gradient.
First you need to specify what direction the gradient is going by providing an angle in radians. 0 is up and pi is down.
The colors will be evenly spaced.
Resize the image to fit the containing element while maintaining proportions and cropping the overflow.
A centered background image that keeps it's natural propostions, but scales to fit the space.
Tile an image in the x and y axes.
Tile an image in the x axis.
Tile an image in the y axis.
Note if you want more control over a background image than is provided here, you should try just using a normal Element.image with something like Element.behind.