#header-outer .cart-menu .cart-icon-wrap .icon-salient-cart,
#header-outer #mobile-cart-link .icon-salient-cart{
 visibility: hidden;
}

#header-outer .cart-menu .cart-icon-wrap,
#header-outer #mobile-cart-link {
  background-image: url('your-icon.png');
  background-size: cover;
  background-repeat: no-repeat;
  background-position: center;
}