.avatar {
  background-image: url('assets/testimonial-avatars.png') !important;
  background-size: 200% 200% !important;
}

.avatar-one { background-position: 0 0 !important; }
.avatar-two { background-position: 100% 0 !important; }
.avatar-three { background-position: 0 100% !important; }
.avatar-four { background-position: 100% 100% !important; }