gb(0, 0, 0)");
  assert_throws_dom('NotAllowedError', iframe.contentWindow.DOMException, () => {
    iframe.contentDocument.adoptedStyleSheets = [nonConstructedStyleSheet];
  });
  assert_equals(getComputedStyle(iframeDiv).color, "rgb(0, 0, 0)");

  iframeStyle = iframe.contentDocument.createElement("style");
  iframe.contentDocument.body.appendChild(iframeStyle);
  iframeStyle.sheet.insertRule(".nonConstructedSpan { color: red; }");
  const iframeStyleSheet = iframeStyle.sheet;
  nonConstructedSpan = docum