Reply To: Style question differently from replies

ok, so for the header you have

#bbpress-forums div.bbp-reply-header
#bbpress-forums div.bbp-topic-header

and on content you have

#bbpress-forums .bbp-topic-content,
#bbpress-forums .bbp-reply-content

You could also download my style plugin

https://wordpress.org/plugins/bbp-style-pack/

and either use that or look at the styles.php file in the css folder for styling css and use what you need.