Depending on your setup you can try installing the “Stylus” addon to your browser with a style such as https://github.com/aclist/kbin-css or https://pastebin.com/b71sNaRe for Lemmy

There’s a lot that can be tweaked from there to get it how you like it, it turns off way too much for my tastes and I haven’t had time to sort it out but it’s a good starting point.