Here's a guide on how to set the size of the main background image in the Divi Theme. Enabling a background image To enable a background image in the Divi Theme, go to the "Divi > Theme Customizer > General Settings > Background > Background Image" option....
background image
Using Shortcodes in the Background Image URL field
The Divi Theme allows you to add background images to Divi Builder sections, rows and modules. By default, Divi doesn't allow shortcodes in the background image URL field. If you want to use a shortcode to generate your background image URL (or part of it), here's how...