✨ Mark some classes as "open" for customizations

### Description

Hey! Thanks for the great NSTextView alternative. Is there a way to have some customization points, either by marking classes as open or by providing public properties? I'm specifically talking about Emphasis - I would like to change the look of the standard ones (to match the app design) by changing the color, removing shadows and adding a rounded border. Or maybe it's already possible but I just did not find? :) Thanks!

### Alternatives Considered

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### Additional Context

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