Description
Changes proposed in this Pull Request
- This PR updates the “Current Theme” bar to the new design as described in #54075.

Testing instructions
- Navigate to
/themes/{SITE_URL}?flags=theme/showcase-revamp
- Verify that the current theme banner displays as indicated above.
- Verify that previous (production) design does not display if feature flag is not enabled.
Related to #54075
Unfortunately, no screenshots were provided by the developer.