Same issue here. I noticed it happened after a recent update. All my notification menus are like this, as well as the "Add to bookmarks" heart menu. It seems the colours are inverted for some reason.
Posts made by Juhca
RE: Dark mode issuesOpera for Mac
RE: [Solved]"Skip to Main Content" showing on every pageOpera for Mac
Same problems here on Mac Catalina. Also made a bug report because it's been driving me crazy.