',
      iframe.contentWindow.DOMException,
      () => { iframe.contentDocument.adoptedStyleSheets = [redStyleSheet]; }
    );
    assert_equals(getComputedStyle(greenIframeSpan).color, "rgb(0, 0, 0)");
    assert_equals(getComputedStyle(redIframeSpan).color, "rgb(0, 0, 0)");
    assert_equals(getComputedStyle(blueIframeSpan).color, "rgb(0, 0, 0)");
    assert_equals(getComputedStyle(whiteIframeSpan).color, "rgb(0, 0, 0)");
    assert_equals(getComputedStyle(yellowIframeSpan).color, "rgb(0, 0, 0)");

    d