You think that's bad, have a look at nova in dark mode:I don't use Safari, but it's not the only app that can be confusing with tabs. For example, Visual Studio Code. To me, the "main.css" tab looks like it's in the foreground (and therefore active), but it's actually the inactive tab.
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Having said that, it's not the end of the world (whether VSC or Safari 15) like some people are acting. You just have to learn the quirks of specific apps.