Dual backgrounds on FontAwesome social icons

example.md

.fa-twitter-square,
.fa-facebook-square {
  position: relative;
  z-index: 0;
}

.fa-twitter-square:after,
.fa-facebook-square:after {
  content: "";
  position: absolute;
  top: 2px;
  right: 2px;
  bottom: 2px;
  left: 2px;
  z-index: -1;
  background: #fff;
}

.fa-twitter-square {
  color: #55ACee;
}

.fa-facebook-square {
  color: #3b5998;
}