Imprimir JS CSS não está funcionando

function printReceipt(el) {
  var w = window.open();

  w.document.write('<html><head><title></title>');
  w.document.write('<link rel="stylesheet" type="text/css" href="css/receipt-print.css">');
  w.document.write('</head><body >');
  w.document.write(document.getElementById(el).innerHTML);
  w.document.write('<script type="text/javascript">addEventListener("load", () => { print(); close(); })</script></body></html>');

  w.document.close();
  w.focus();
}
SECRET MYSTERY