Here is a small snippet to change your background-color into a great image.
Just like this: Hover me
To do that, disable the general background of your app and optionally disable the header background:
add the following css in the “advanced customization” section of your editor:
Obviously you have to change the url code “http://i.imgur.com/jyeOuJh.jpg” for your own.
To get the best result, choose an image with a portrait format.
That modification changes all of yours features’ backgrounds.