code: function(id, cssString) {
          var style = document.createElement('style');
  
          style.type = 'text/css';
          style.id = id;
  
          if (style.styleSheet) {
              style.styleSheet.cssText = cssString;
          } else {
              style.appendChild(document.createTextNode(cssString));
          }
  
          document.getElementsByTagName('head')[0].appendChild(style);
      }
docs: create style element and append it into the head element.
  @param {String} id - element id
  @param {String} cssString - css string