#7848908 Theme Showcase: Logged-out header

Related to #73266

Proposed Changes

This PR updates the Theme Showcase logged-out header as described in #73266. The update is only for the logged-out header, so the logged-in header should remain unchanged.

Before	After

Before	After

@davewhitley @vinimotaa @david-gonzalez-a8c

Testing Instructions

• Head to the logged-out Theme Showcase and ensure that the header is as described above.
• Ensure that the logged-in Theme Showcase header works the same as before.

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the “[Status] String Freeze” label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
• For changes affecting Jetpack: Have we added the “[Status] Needs Privacy Updates” label if this pull request changes what data or activity we track or use (p4TIVU-ajp-p2)?