li button.icon-webrtc-voice:before {
  background-image: url(/contacts/style/webrtc-client/images/actionicon_contacts_webrtc_audio.png);
  background-size: 3rem;
}

li button.icon-webrtc-video:before {
  background-image: url(/contacts/style/webrtc-client/images/actionicon_contacts_webrtc_video.png);
  background-size: 3rem;
}