Fonts (Boot package): mobile masterbar covers Fonts page header

[simison]

Related to #70862

Description

The masterbar on mobile covers the header of the page created using WP Build and Boot package.

I can replicate the issue with just using WP build to create custom pages, so the issue isn't Fonts page specific, it's Boot package specific.

The buggy container has the same common.css WP styles as the editor (where this works), so I'm not sure what the issue is:

Step-by-step reproduction instructions

• Go to Appearance → Fonts
• Enable mobile viewport
• Note how "Fonts" header disappears

Screenshots, screen recording, code snippet

Desktop

Mobile

No such issue with site editor pages (they don't have the masterbar) nor editor:

Environment info

• Gutenberg trunk
• Assembler theme

Please confirm that you have searched existing issues in the repo.

• Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

• Yes

Please confirm which theme type you used for testing.

• Block
• Classic
• Hybrid (e.g. classic with theme.json)
• Not sure

FYI @youknowriad