Scope variable and CSS definition to the admin styles

To remind of some coordination with moving the related styles from Top Bar 📌 Create feature flag module to control navigation top bar visibility Fixed also in progress.

Fixed in core MR directly
https://git.drupalcode.org/project/drupal/-/merge_requests/7474/diffs?co...

Closing this then. Let's open a MR for any follow-up.

Automatically closed - issue fixed for 2 weeks with no activity.