Edit the Members Avatar without Avatar Groups

I want to know how to change the css of the avatar members without to change the css avatar groups.
i use a buddypress child theme:
this is the link for my web Site:
For the Members page: http://www.ikomor.com/members
and for Groups: http://www.ikomor.com/groups
to do same think like this:

member Avatar circle.
and Groups Avatar Square.
the Screenshot