Adjust CSS for new global dark mode setting per user

Problem/Motivation

The dark mode setting per user brings in a new data-color-scheme for the html tag. The CSS data for making the left navigation and the top bar dark when required, currently lives in the default_admin theme. This should be brought over to the navigation module.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet