Using Background Overlap
If enabled (the default), the background will fill the entire screen and the Page element will simply overlap it (partially obscuring it as a result). If disabled, the Page element will not overlap the background, and instead scale the latter to fill the remaining space on the screen. Disabling this is recommended if the background is set to something important.
If enabled, the width of the Page element will be constrained on smaller and mobile screens to show as much of the background as possible. If disabled (the default), the Page element will simply use its defined Width regardless of screen size. Enabling this is recommended if the background is set to something important.