Hide the `findBarView` border like Mail

How to hide the findBarView shown on ⌘-F border the same way it is done in Mail in the window to compose message? This should be possible with the SDK of macOS 11.

The findBarView correctly appear in the scroll view area, but has a separator between text content and the find-bar.

I made a mistake, the application I compare this feature is not TextEdit but Mail. (This mistake was fixed)

Hide the `findBarView` border like Mail
 
 
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