Default page backgrounds based on theme

We need a default page background option to reflect and respect the user’s theme automatically. When I’m using Dark Mode and no specific page background color is set, it should default to #1E1E1E, while for someone using Light Mode the page background should be #F5F5F5.

I imagine something like a simple toggle “Use background color based on theme“ or something like this, as the default, with the option to set a custom background color that becomes the background color for everyone.