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