To save mobile data, video backgrounds for sections are disabled for mobile site viewing. Other background options, though, are available for mobile render such as colors and images.
Moreover, any video background you would initially set for a section would only apply for desktop view, by default, and no section background will appear for the mobile version of the same site.
To set a section background for mobile render:
1. Select the section you want to add mobile render background for.
2. At the bottom of the left editing panel, select which type of section background you want to set under Mobile Background.
3. Follow through the prompts depending on which type of background you would choose.