Customize the background of your website by choosing a color or image. Your background can be customized per device.
Click the design option in the menu on the left sidebar.
Choose Background Image & Color then move your cursor over the device you'd like to change the background of. For 'All Devices' you can choose a color or background image.
For tablet and mobile, you can select an image.
The content background is available too for some themes. This corresponds to the area of your site behind the content area, but above the main site background. In the image below, the yellow color is the content background, while the trees are the image used for the site background.
You can set content background for the homepage and inner pages separately.