<head>
<script>
function test()
{
    const link = document.createElement("link");
    link.setAttribute("rel", "stylesheet");
    link.setAttribute("href", "data:text/css,body { background:white !important; }");
    document.head.appendChild(link);
    const count = document.styleSheets.length;
    document.body.innerHTML = (count == 1) ? `PASS` : `FAIL: document.styleSheets.length == ${count}`
}
</script>
<link rel=stylesheet href="data:text/css,body { color:black !important; }">
</head>
<body onload="test()" style="color:blue; background:red">