ame.sub.html?html-writing-mode=${writingMode}&container-writing-mode=${containerWritingMode}&dialog-writing-mode=${dialogWritingMode}&dialog-width=${dialogSizes[0]}&dialog-height=${dialogSizes[1]}`;
      iframe.width = iframeWidth;
      iframe.height = iframeHeight;
      iframe.onload = t.step_func_done(() => {
        const dialog = iframe.contentDocument.querySelector("dialog");
        const dialogRect = dialog.getBoundingClientRect();

        const expectedLeftOffset = iframeWidth / 2 - dialogRect.w