      myCE.elementInternals.states.add('--foo');
        t.add_cleanup(() => { myCE.elementInternals.states.clear() });
        assert_true(myCE.elementInternals.states.has('--green'));
        assert_true(myCE.elementInternals.states.has('--foo'));
        assert_equals(getComputedStyle(myCE).getPropertyValue('color'), 'rgb(0, 255, 0)');
        myCE.elementInternals.states.clear();
        assert_false(myCE.elementInternals.states.has('--green'));
        assert_false(myCE.elementInternals.states.has('--f