Interesting. On #Windows, I upgraded #Vivaldi and the tabs look completely the same. Mac version fiddled the tab visuals. Not sure what is different configuration-wise. Will look into it later.

@dhry Are you referring to the new floating tabs style? Not sure either why you only got them on macOS but not on Windows.

Either way, if you don't like them, you can always disable them in either platform from vivaldi://settings/appearance/ -> User Interface Density -> Select "Compact".