Site Editor: Unwanted top margin added to the first block inside flow layout container

[iamtakashi]

Description

This must have been introduced recently. It only happens when the Gutenberg plugin is activated and seems to happen only in the site editor.

Usually, when the layout is constrained, the top margin is removed from the first block in a container.

However, if the container has the flow layout, the top margin doesn't get removed.

Step-by-step reproduction instructions

1. Open the site editor
2. Add a group block
3. Add a block in the group block
4. Set the layout of the group block to flow(unconstrained).
5. See the gap between the container and the first block in it.

Screenshots, screen recording, code snippet

No response

Environment info

• WP 6.5.3
• Gutenberg trunk

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

[tellthemachines]

Hmm, looks like there's an extra curly bracket being output in the global styles for the site editor:

Edit: yeah this was introduced by #60715. I'll put up a quick fix!