Site editor modal on small viewports respects invisible admin bar

[draganescu]

Description

When using the site editor the preferences modal leaves room at the top for an invisible admin bar. This works in the post editor (although even there it's weird) but in the site editor looks quite broken.

Step-by-step reproduction instructions

1. Enter responsive design mode / use a small screen device
2. Go to the site editor
3. Tap the dot menu in the top right corner
4. Tap "Preferences"
5. Notice the top space

Screenshots, screen recording, code snippet

Post editor	Site editor
Top space admin bar visible	Top space site editor header

Environment info

No response

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