Background images for page sections and for nested rows (section is a top level row in the page builder) can be set in the page builder row settings inside X40 Design section.
Background images inside page section are displayed with parallax effect. Background images inside nested rows are displayed without parallax effect.
Backgrounds for common elements like footer and comments and for default page layout can be set via page builder also, via
Appearance / Widgets in the WordPress Administration Panel. See Default Layounts, Default Layounts, Comments. This backgrounds can be overrided in the page settings on page editor bottom. The options
Override Default Content Backgrounds,
Override Footer Backgrounds,
Override Comments Backgrounds for this purpose.