make UI more consistent with core WP

[psorensen]

Description of the Change

This update moves makes the interface more consistent with the core UI by consistent padding to the toolbar button and popover element.

Before:

After:

Closes #231

How to test the Change

• Add new paragraph text
• Press cmd + o to toggle character inserter
• Observe proper padding in both toolbar button and popover item

Changelog Entry

Added - New feature
Changed - Existing functionality
Deprecated - Soon-to-be removed feature
Removed - Feature
Fixed - Bug fix
Security - Vulnerability

Changed UI to have padding consistent with WP Core

Credits

@psorensen @fabiankaegy

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests pass.

[fabiankaegy]

This is a nice little improvement and the code look good to me :)

I was unaware by how much of the UI is coming from the Library we are using here. That is a real bummer. But still this is a step in the right direction :)