Fix mobile toggle placeholder overlapping issue

[MDSAM05]

Summary

This PR fixes an issue where the placeholder element overlaps the second list item on mobile devices when the first toggle list item is collapsed.

Rationale

• On screens ≤ 600px, the .ProseMirror-trailingBreak placeholder was positioned incorrectly, causing visual overlap.
• This affected usability when editing toggle lists in mobile view.

Changes

• Added responsive CSS to reposition the trailing placeholder element.
• Ensured placeholder displays inline and maintains proper spacing on mobile.
• Updated Block.css with a mobile-specific rule:

  .bn-inline-content:has(> .ProseMirror-trailingBreak:only-child)::before {
    position: relative !important;
    top: 0 !important;
    left: 0 !important;
    margin-left: 4px !important;
    display: inline-block !important;
    line-height: inherit !important;
  }
}

Impact

• No breaking changes.
• Desktop behavior is unchanged.
• Fixes overlapping visual bug for mobile users.

Testing

• Manual tests performed:
• Created a toggle list with multiple items.
• Collapsed the first item.
• Verified no overlapping placeholder text on mobile viewport (≤ 600px).

Screenshots/Video

Before

After

Checklist

• [ x] Code follows the project's coding standards.
• Unit tests covering the new feature have been added.
• All existing tests pass.
• [x ] The documentation has been updated to reflect the new feature

Additional Notes

[vercel]

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