Flarum will have this functionality once it is ready for prime. But right now it isn't really ready to be used in a production environment.

I've gotten use to it. It isn't actually that bad. With that said, I believe it would be pretty easy to make a theme that doesn't use that style. I was planning to look into it later this weekend with everything else I am doing and release it sometime next week as nodebb-theme-classic. That doesn't mean I actually will, since I tend to get pretty lazy over weekends. But I will try, and if it is easy you may just get something more classic styles.