Current toolbar font is not available with most operating systems

Problem/Motivation

The current toolbar font Source Sans Pro is not available (by default) with most operating systems. This leads into the backup font Lucida Grande and Verdana being used with most users. When a theme provides Source Sans Pro as a custom font, it may result in an inconsistent experience between the frontend and the admin area of the site. This is the case when Umami and Claro are being used.

Proposed resolution

A potential solution would be to use system fonts for the toolbar to remain consistent with the Drupal design system.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet