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