BuddyPress.org

Have you every used Firebug before (it’s a Firefox addon). Install it and then you can inspect which class you are trying to hide.

That code looks to be for a widget, not a menu.

Once you figure out what you are trying to hide, download something like this so you don’t have to keep making the change everytime your theme updates https://wordpress.org/extend/plugins/safecss/

Then put

whateveryouarehiding {display: none;}

to hide the menu.