Update logged-out Theme Showcase header

[autumnfjeld]

Description

This is the current LoTS header:

Instead we want something like:
From pdgAPm-yE-p2#comment-649

Tasks

• Cordinate with Vini &/or David Gonzalex &/or Dave Whitely to get ready-for-build design. See thread pdgAPm-y@Automattic/lego
• Finalize copy Theme Showcase: Logged-out header #74241 (comment)
• Update header

@davewhitley @vinimotaa @david-gonzalez-a8c @Automattic/lego

[davewhitley]

Design

It's helpful to look at what the mobile design looks like for Plugins

If we can reuse the same implementation as Plugins, that would be great!