function injectStyleSheet(cssText) {
  var $style = document.createElement('style');
  var css = document.createTextNode(cssText);
  var container = document.getElementsByTagName('head')[0];
  $style.type = 'text/css';
  if ($style.styleSheet) {
    $style.styleSheet.cssText = css.nodeValue;
  }
  else {
    $style.appendChild(css);
  }
  if (!container) {
    container = document.getElementsByTagName('html')[0];
  }
  container.appendChild($style);
}

// workflowyを開いたときだけ
if (/workflowy\.com/.test(location.host)) {
  // injectStyleSheet("ここにCSSを書き込む");
  injectStyleSheet(".contentUnderline{border-bottom: 2px #0000FF solid;text-decoration:none;}.contentBold{border-bottom:2px #f00 solid;}.contentItalic{background-color:#bf9;text-style:normal;}");
}