Opera for mac have very soft and gray (lack of contrast) fonts for tabs (in screenshot attached, first is firefox, second opera; in firefox title font is black and sharp, in opera is washed and fade - no, opera is not in the background).
Also, dark mode is very dark, black is too deep and active tab too hard to see.
Mac os H.S. 10.13.
In windows 10, the issues doesn't exist, everything is fine.