[Block] Navigation nested inside [Block] Cover results in Z-Index issues with other cover blocks

[cuemarie]

Description

If a navigation block is nested in a cover block, the navigation's submenu overlay overlaps with other Cover blocks on the page in the editor as well as in the live site. This overlapping breaks the links of the overlay menu, and makes the submenu close when you try to hover over links.

Step-by-step reproduction instructions

1. In an FSE theme, open the site editor
2. Insert a Cover Block, then nest a Navigation Block inside that Cover block
3. Add a 2nd Cover block after the first
4. Turn on the Navigation's Overlay Menu and test it in the editor and the live site
5. You can also see the same behavior with a submenu

Screenshots, screen recording, code snippet

Editor Behavior

Screen.Capture.on.2023-04-07.at.14-11-24.mov

Live Site Behavior

Screen.Capture.on.2023-04-07.at.14-20-26.mov

Environment info

• Replicated in Wordpress 6.2 with Gutenberg deactivated
• Replicated with Gutenberg versions 15.4.0 and 15.5.0 active as well
• Theme used for testing: Twenty Twenty-Three

Originally reported here: Automattic/wp-calypso#75439

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

[kathrynwp]

I was able to replicate this with:

• WP 6.2
• Gutenberg 15.5.0 active or inactive
• No other plugins active
• Twenty Twenty-Three 1.1

[kathrynwp]

I think this may be a duplicate of #45353. @cuemarie, what do you think?

[cuemarie]

@kathrynwp yep, looks like the same symptoms in their recordings and report. Thanks for that find - I'll close this n favor of that one!

[entlein007]

I beg your pardon. I experienced an issue with a dropdown to a Navigation Block within a Cover Block on a live site. It displays underneath the following Main Section.
That behavior showed up when I updated to WP 6.3.1. No Gutenberg-Plugin installed. I read in your post that a z-index issue pertaining to the Cover Block was already addressed (In Gutenberg plugin only or also in Core?) What do I need to do to use the fix? I went back to an earlier WP Version to get a quick fix to my problem in the meanwhile. I am just a theme-user, first-timer on git-hub, not a developer, not sure how to address this.