Well, fuck.

One of the main reasons I switched to Vivaldi a few years ago was that it allowed and even advertised a "classic" browser experience. By which I mean: tabs that behaved like tabs, visual separation, not a lot of useless whitespace and corner-radius-maxxed borders everywhere.

Looks like that's all gone now and Vivaldi is just yet another generic "flat design" browser. Time to look for something else...