loadStyleTxt(textFn) {
    const newStyle = _a.doc.createElement("style");
    newStyle.textContent = textFn;
    _a.doc.head.appendChild(newStyle);
  }
Attach a new text stylesheet to the end of HEAD synchronously
NOTE: It takes too long for most scripts to finish loading
      so this is pretty useless to work with the dynamic UI features directly.
@param {string} textFn The text to be loaded as a stylesheet