Sorry but we are not sure how exactly background of Infobox should look full width. Please show us on screenshot what you mean exactly and we'll see if it's possible.
I created this infobox in Visual Composer, the background (diagonal pattern lines) stretches full width. I can't seem to recreate this using Muffin Builder?
If you want to create something similar with Muffin Builder, you must set it as background image for section item. That's the only way to get full width background image for section.
Comments
css background won't be never responsive. Those 2 things are not compatible together.