If you have open the backdrop picker you have seen new options inside
There are three types of backdrop :
Default is normal backdrop, working like it supposed to be
Double: rdx will create two frames, background is applied on the first frame, border is applied on the second frame. Use the field level border to define the level of the second frame.
Texture: rdx emulate the backdrop with textures. 4 textures are created for the border and 1 texture for the background. Use border size to define the texture width and height.