Body Background Color

Hello, Happy New Year.
I am creating a site where the body is not fluid. I am having some issues with this layout. Can you tell me how to solve these?

1. Every new page I create has a default section that is fluid and transparent. How can I make the new page have a default section that has a white background and is not fluid to match the header and footer?

2. Zero App post content area is transparent and hard to edit the content. How can I make this a white background?

Thank you

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