Found this really simple and clean CSS solution to adding new window icon.
a[target="_blank"]::after {
content: "";
width: 1em;
height: 1em;
margin: 0 0.05em 0 0.1em;
background: url(data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHZpZXdCb3g9IjAgMCAxNiAxNiIgd2lkdGg9IjE2IiBoZWlnaHQ9IjE2Ij48cGF0aCBkPSJNOSAyTDkgMyAxMi4zIDMgNiA5LjMgNi43IDEwIDEzIDMuNyAxMyA3IDE0IDcgMTQgMlpNNCA0QzIuOSA0IDIgNC45IDIgNkwyIDEyQzIgMTMuMSAyLjkgMTQgNCAxNEwxMCAxNEMxMS4xIDE0IDEyIDEzLjEgMTIgMTJMMTIgNyAxMSA4IDExIDEyQzExIDEyLjYgMTAuNiAxMyAxMCAxM0w0IDEzQzMuNCAxMyAzIDEyLjYgMyAxMkwzIDZDMyA1LjQgMy40IDUgNCA1TDggNSA5IDRaIi8+PC9zdmc+) no-repeat;
background-size: contain;
display: inline-block;
vertical-align: text-bottom;
}
Source and Demo: https://stackoverflow.com/a/65370632/