How do i embed a gallery as a page background with header and footer?

The way i have been doing it works on the live page but when i go back to the editor the gallery is on top and the content is below it. I had to remove the header and footer and put nav menu at top and footer content at bottom. makes it hard to create new pages with continuity because i have to cut and paste header and footer each time. any suggestions? i apologize if this subject was already discussed.

thanks !

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