@whisperer Apparently they purposely hang on to the white address bar in darkmode for some unknown reasons(?) Even the possibility Leocg mentioned above might be true, like, some of them really think the private mode should be visually standout compare to normal mode, and standout in white
It's just super weird, because instead of providing a different dark color theme for private mode to make it distinguishable from normal mode, they decided to choose a white color for dark theme. It doesn't make any sense. If there're 2 separated color themes, one for light and one for dark according to windows theme, then white bar should only appear in light theme of opera, not dark one. There's zero sense to this color choice of pure white at all. It's all messed up.
If they're too stuck up with the idea of private mode theme need to be distinguishable from normal mode theme, then do in the way Brave or Vivaldi did. They have private/incognito mode in distinguishable color theme, and still suitable for dark theme. Of course the color choice of Brave or Vivaldi (private mode) might not fit to everyone taste, but in general, it's still better than pure white. Opera One pick the worst choice of color, by far.