If you want to add a different background to a specific page, you can do it via Post Options section in the Page Editor.
Note: Post Options section will appear on the page backend only after you have installed the plugin Advanced Custom Fields PRO. It’s bundled with Jupiter X and can be installed via Jupiter X > Control Panel > Plugins as described in this article.
To add a background to a specific page
1. From the WordPress left dashboard menu, go to Pages and open the page you want to add a different background to.
2. In Post Options open Main tab and under Styles section, you can choose a Background Image or a Background Color for your page and set the properties.
3. Publish or Update the page.