Adjust z-index for section dividers

[Soare-Robert-Daniel]

Closes #1751.

Summary

Adjust section dividers so they can be behind the content but in front of the background.

Screenshots

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Test instructions

1. Make a section block with content.
2. Insert the dividers.
3. Ensure the dividers are behind the content but in front of the Section background.

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Checklist before the final review

• Included E2E or unit tests for the changes in this PR.
• Visual elements are not affected by independent changes.
• It is at least compatible with the minimum WordPress version.
• It loads additional script in frontend only if it is required.
• Does not impact the Core Web Vitals.
• In case of deprecation, old blocks are safely migrated.
• It is usable in Widgets and FSE.
• Copy/Paste is working if the attributes are modified.
• PR is following the best practices

[pirate-bot]

Bundle Size Diff

Package	Old Size	New Size	Diff
Animations	192.38 KB	192.38 KB	0 B (0.00%)
Blocks	1.34 MB	1.34 MB	0 B (0.00%)
CSS	6.9 KB	6.9 KB	0 B (0.00%)
Dashboard	44.4 KB	44.4 KB	0 B (0.00%)
Export Import	4.7 KB	4.7 KB	0 B (0.00%)
Pro	225.44 KB	225.44 KB	0 B (0.00%)

[pirate-bot]

Plugin build for a564d84 is ready 🛎️!

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[pirate-bot]

E2E Summary

Typing

Test	Average Time (ms)	Standard Deviation (ms)	Median Time (ms)	Quantile for soft limit (%)	Quantile for hard limit (%)
Typing	51.29	8.09	49.2	89.47 (60ms)	100 (80ms)

Values above 60ms

"1 - 79.69, 5 - 61.57"

[rodica-andronache]

@Soare-Robert-Daniel everything's working well 🚀

[pirate-bot]

🎉 This PR is included in version 2.3.4 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀