using gutenberg and FC together - looking for advice.

I have a handful of pages that will have to be gutenberg pages. This raises two issues I see that I could use some guidance or creative workarounds on.

1. Staying inside the FC theme (for lack of a better term). Within FC there is a top nav and side nav, when you render different FC pages they stay inside of that theme, retaining the nav. I need to create some gutenberg pages which will be linked in the top nav, how do I get them to render inside the FC theme rather than opening a separate wordpress page, losing the top/side nav?

2. light/dark mode - I want to offer the light/dark mode switch for users, but for the pages outside of FC, the gutenberg pages, this breaks. Even with a Gutenberg theme with dark mode it would require a user to click in two places to enable it. Any workarounds here?

   Deploying away from BB, Elementor Pro, and Learndash this weekend, appreciate how helpful this community has been.