<head>
<style>
@import url("resources/css-insert-import-rule.css");
div {
    width: 100px;
    height: 100px;
}
</style>

<script>
function test() {
  document.styleSheets[0].insertRule('@import url("resources/css-insert-import-rule.css");', 0);
}
</script>

</head>
<body onload="test()";>
<div></div>
</body>