If you added a background image to the map in the "resource" tab you can change the opacity of the tile and move the background.
- A resource can be an image that you will be able to use as terrain or as a background for the map (in this case you might want to use the "opacity" feature). The text field can be filled with any any valid CSS color.
- A resource can also be a saved map in which case you will be able to add it to the "Submaps" tab.
With a premium account you can save your maps on the server and use them anywhere. This functionality is in beta and is only available to a few users.