1. Go to Page Background (or Section Background)
The page background function can be found in the Settings menu of your page:
In order to get to the Section background settings, hover your pointer outside the editable zone of the page, and click on the Edit button:
2: Select, buy, or upload an image:
3: Set the background image to Stretch from the menu.
And that’s it. Now your background image is responsive, adapting its width to your visitor’s screen size.