<!doctyle html>
<style>
:is(.test1) { color:green; }
:is(.test1, .test1::before) { background-color:red; }
:is(.test2)::before { color:green; content:'Test that :is() is invalid if it contains a pseudo element'; }
:is(.test2::before) { background-color:red; }
:where(.test3) { color:green; }
:where(.test3, .test3::before) { background-color:red; }
:where(.test4)::before { color:green; content:'Test that :where() is invalid if it contains a pseudo element'; }
:where(.test4::before) { background-color:red; }
</style>
<div class=test1>Test that :is() is invalid if it contains a pseudo element</div>
<div class=test2></div>
<div class=test3>Test that :where() is invalid if it contains a pseudo element</div>
<div class=test4></div>