Unfortunately Opera has become a dry hump since it became just another Chromium fork. There's little to link it with the old Opera (Presto). Although there are (very) subltle differences, it's basically Chrome with an Opera badge. It's no longer customizable in any real sense of the word.
You may wish to look at Otter http://otter-browser.org. "Controlled by the user, not vice versa", they say. Sound familiar? And it's their aim to "...recreate the best aspects of the classic Opera (12.x) UI using Qt5." It's still in beta, but getting a lot of love and support 