<!DOCTYPE html>
<!-- Nested fieldsets should be assigned validation correctly -->
<html>
<head>
<style>
fieldset:valid { background-color: green; }
fieldset:invalid { background-color: red; }
</style>
</head>
<body>
<fieldset>
<fieldset>
<input>
</fieldset>
<fieldset>
<input required>
</fieldset>
</fieldset>
</body>
</html>