Fix Z-Index Issue for Link Options in Block Editor

[dhananjaykuber]

Fixes #63795

What?

This PR adds a z-index to the .editor-visual-editor class to prevent link options from being hidden when editing text at the bottom of the page.

Why?

Currently, when editing text at the bottom of the page in the new block editor, the link options can be hidden behind other elements (such as SEO options). This issue occurs because the .editor-visual-editor class lacks a z-index property. Adding a z-index resolves this problem and improves the user experience when working with links in the editor.

How?

The fix involves adding a z-index: 20 to the .editor-visual-editor class in the appropriate CSS file. This ensures that the editor's content, including link options, appears above other page elements.

Testing Instructions

1. Go to "Add New Post"
2. Add a long block of text that extends beyond the initial viewport
3. Scroll to the bottom of the text
4. Try to add or edit a link in the text at the bottom of the page
5. Verify that the link options are visible and not hidden behind other page elements

Screenshots or screencast

[github-actions]

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[t-hamano]

Hi @dhananjaykuber,

This issue has been resolved in #63939. Of course, you have been added as a co-author to the props.

I would like to close this PR, but thank you for your efforts!