If there's no topic tags input, "Add topic" button is a bit going up due to

#wpforo #wpforo-wrap .wpf-topic-create input[type=submit] { margin-top : -5px; }

Could you add some margin-top on style.css?

#wpforo #wpforo-wrap .wpf-topic-create input[type=submit] { margin-top : 5px; }

I hope you support customized style.css under theme like Buddypress.

Thank you 🙂