Describe the bug

This seems to fail on themes like Twenty Nineteen which offers a full width editor.

First reported in the support forum. Props to @burnuser

Steps to Reproduce

1. Set TwentyNineteen as the active theme
2. Create a Post and add some text content
3. Move the cursor to the start of the text and open inserter popup
4. Observe it hides behind the admin sidebar

Screenshots, screen recording, code snippet

WordPress information

• WordPress 5.9
• Insert Special Characters 1.0.3

Code of Conduct

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