int addRule(String selector, String style, [ int index ])

Source

int addRule(String selector, String style, [int index]) {
  if (index != null) {
    return _blink.BlinkCSSStyleSheet.instance
        .addRule_Callback_3_(this, selector, style, index);
  }
  return _blink.BlinkCSSStyleSheet.instance
      .addRule_Callback_2_(this, selector, style);
}