Removing dark borders from UI elements, including windows and buttons

Question

I have somehow managed to configure my Mac to display dark borders around windows, toolbar buttons, and other UI elements, as you can see in the screenshots below:

All apps are now showing borders like this. How can I remove them?

Answer 1

You have turned on ‘Increase contrast’ in settings.

Open System Preferences, search for ‘contrast’ and unselect ‘Increase contrast’: