FYI: regular Firefox for Android also has reader mode.
I still quite like Firefox Preview though. I'm not quite sure what you mean by CSS theme-color, but if that refers to preferes-color-scheme: dark, then as far as I can see it supports that? DuckDuckGo is dark for me.
I still quite like Firefox Preview though. I'm not quite sure what you mean by CSS theme-color, but if that refers to preferes-color-scheme: dark, then as far as I can see it supports that? DuckDuckGo is dark for me.