.nav-social__item a {
  background-size: 14px 14px;
  display: block;
  height: 14px;
  width: 14px;
}

.nav-social__item.is-twitter a {
  background-image: url('../images/nav-twitter@2x.png');
}

.nav-social__item.is-instagram a {
  background-image: url('../images/nav-instagram@2x.png');
}