Create new site-wide visual styles for off-canvas dialog

Background

Within #3291797: Refactor Drupal 10 settings tray / off-canvas to use modern CSS, we're refactoring all of the styles for the off-canvas dialog. This also includes a proper reset, so the styles will look the same across all themes. This issue also removes customizations of styles within Claro, and Olivero (which were mostly fixes)

Claro currently overrides the look and feel of the off-canvas, but it only does this when the Claro theme is enabled.

Task

This ticket is for the design portion of the task. We need to create designs that will be "on brand" for Drupal within all themes (core and contrib).

Followup

The implementation of this will be in a followup ticket, but should be straightforward using the new CSS custom properties and selectors defined in the refactoring issue.