external_link_css.php

/**
 * Add external link CSS to the head
 */
function external_link_css() {
  echo '
  <style>
    a:after {
      content: "\e9a7";
      margin-left: .3em;
      font-size: .8em;
      font-family: "icomoon" !important;
      speak: none;
      font-style: normal;
      font-weight: normal;
      font-variant: normal;
      text-transform: none;
    }
    a[href^="'.site_url().'"]:after,
    a[href^="#"]:after,
    a[href^="skype:"]:after,
    a[href^="tel:"]:after,
    a[href^="mailto:"]:after,
    a:not([href]):after {
      content: none;
    }
  </style>';
}
add_action('wp_head', 'external_link_css');