   assert_throws_dom('NotAllowedError', () => { document.adoptedStyleSheets = [iframeRedStyleSheet]; });
    assert_equals(getComputedStyle(greenSpan).color, "rgb(0, 0, 0)");
    assert_equals(getComputedStyle(redSpan).color, "rgb(0, 0, 0)");
    assert_equals(getComputedStyle(blueSpan).color, "rgb(0, 0, 0)");
    assert_equals(getComputedStyle(whiteSpan).color, "rgb(0, 0, 0)");
    assert_equals(getComputedStyle(yellowSpan).color, "rgb(0, 0, 0)");

    iframe.contentDocument.adoptedStyleSheets = [iframeRed