Why does the basic Opera in the dark theme have an ugly white border in the context menus (context menu pages, tabs, tab bar, address), Opera Menu, etc., and Opera GX does not have it?
Basic color is only black? Why? Please. add choice basic color - black or white/silver.
In my experience in the past this related to ad blocking, maybe it is in this case, maybe not. I probably won't be back here but thought maybe that you can disable ad blocking or any extensions related to it. Hope it helps but if not, sorry and hope you get it sorted.
Other common suggestions are to clear cache and flush your DNS. These might be helpful as well.