Changing the default background image

Hi,

I have found the the app theming to adjust the themes. I have set the log in screen image however I would like to set a different image for the background screen after log in. When i select the image for the log in screen, both the log in and the dashboard backgrounds change together.

Is it possible to set a new default bg for all users?

also, as soon as i enable theming the top menu bar dissapears alltogether. Is this a bug or is there a setting for this somewhere?