The name of the widget is "MarlinViewOverlayBar". The problem is that it has a built-in CSS stylesheet that is not overridable from the user's theme. I will lower the priority of that stylesheet and mark this bug as fixed for pantheon-files.
The name of the widget is "MarlinViewOver layBar" . The problem is that it has a built-in CSS stylesheet that is not overridable from the user's theme. I will lower the priority of that stylesheet and mark this bug as fixed for pantheon-files.