<!DOCTYPE html>
<html>
<title>The :unresolved pseudoclass reference file</title>
<link rel="author" title="Aleksei Yu. Semenov" href="mailto:a.semenov@unipro.ru">
<style>
    body {
        background-color: white;
    }
</style>
<body>
    <p>Test passes if x-element background below is red</p>
    <a is="x-element" style="background-color: red;">
        x-element
    </a>
</body>
</html>