Old Opera (running Presto like what I have) doesn’t do content-box stuff. Our old webshops had
{box-sizing: content-box;}
this broke everything on Opera, IE and who knows what other browsers. I removed it, all of it.
I’ve also had to explicitly override content-box for Chrome and Blink browsers which is added by the browser stylesheet to buttons, which did not allow me to correctly width and style buttons in widgets.
content-box is a shortcut for people who could never wrap their heads around the original box model. I suggest trying your images without it, and seeing if it works better (simply because, possibly the version of Opera you’re looking at does not support this… current versions of Opera should, because they’re now Blink browsers and Blink supports the content-box stuff).