fix(slate-react): add top css to placeholder

[horacioh]

Description
Placeholder position in Safari 16.4 is not correct. this PR aims to fix that. I also checked that in other versions of Safari there's no regression.

Issue
Fixes: #5386

Example
Before:

After:

Checks

• The new code matches the existing patterns and styles.
• The tests pass with yarn test.
• The linter passes with yarn lint. (Fix errors with yarn fix.)
• The relevant examples still work. (Run examples with yarn start.)
• You've added a changeset if changing functionality. (Add one with yarn changeset add.)

[changeset-bot]

🦋 Changeset detected

Latest commit: 9239ba6

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
slate-react	Patch

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[Arkellys]

Isn't this change too specific to Slate docs? It breaks my placeholders.

[jasontlouro]

Breaks ours as well, completely ignores padding on the editor.

[jasontlouro]

Sounds like a job for...

😅

[heyitsaamir]

+1. Can we revert this? It's leading to a worse experience for most cases (i.e. atleast on chrome, it breaks like others have mentioned, even if it works on safari)