How to change the background color or add image as background in DW Page Modern?

Hi,
If you want to change the background color or background image, you can override the image in the wp-content\themes\dw-page\assets\img folder. If you want to change the background color, you can add the style.css that you have used in the DW Page Modern to the stile.css file of DW Page.
If you have any issue, you can send me your site URL, I will check and help you resolve it.
Hope this helps !