unction assertPseudoElementProperty(originatingElement, pseudoType, backgroundColor) {
    const pseudoStyle = getComputedStyle(originatingElement, pseudoType);
    const pseudoBackgroundColor = pseudoStyle.getPropertyValue('background-color');
    assert_equals(pseudoBackgroundColor, backgroundColor, pseudoType +
      " background-color should be " + backgroundColor.toString() +
      " but was " + pseudoBackgroundColor.toString());
  }
  promise_test(async () => {
    await waitForAnimationFrames(2);
   