If you want to change Dark Theme color you need to follow the below process.
How to Change Dark body Color?
Please follow the below steps to change Dark body Color
Step 1 :
Make sure the theme is set completely to dark mode by adding the following attributes to the html tag
data-theme-mode="dark" data-header-styles="dark" data-menu-styles="dark"
Step 2 :
To change Dark body Color you have to open _variables.scss file and replace what color you want as shown in below