Is there a way to make Opera use just the current desktop theme so that it looks the same as other apps? Google Chrome has the "use Gtk theme" setting for that, and when I copy Chrome's Preferences file into Opera's settings directory I get comparable but not perfectly equal behaviour. It's close to what I want, but see below, and the scroll bars look like they would on MS Windows 3 ...
The settings page suggests I'm using what appear to be an empty theme; I don't think entry would be shown in a fresh install.

NB: both also show a surprising colour as the background in the tab bar, which seems to be related to my selection colour. Does anyone know how that background appearance is determined?