Toolbar doesn't stay fixed properly for non-admin users

Problem/Motivation

For users that are allowed to use toolbar but are not otherwise given any other admin permissions, the toolbar doesn't stay fixed properly. The toolbar looks like it keeps a bottom border and shadow, but not the rest of the actual toolbar, such as the username. There's no issue for admin though.

Steps to reproduce

1. Install Drupal 9.4
2. Add a regular user with no roles
3. Enable "Use the toolbar" permission for authenticated users
4. Login to the regular user and see that the toolbar doesn't stick properly when scrolling

Proposed resolution

Remaining tasks

Add tests

User interface changes

Before:

After:

API changes

Data model changes

Release notes snippet