code: function _getPropValue(element, propName) {
      var propValue = '';
      if (element.currentStyle) {
          //IE
          propValue = element.currentStyle[propName];
      } else if (document.defaultView && document.defaultView.getComputedStyle) {
          //Others
          propValue = document.defaultView.getComputedStyle(element, null).getPropertyValue(propName);
      }
  
      //Prevent exception in IE
      if (propValue && propValue.toLowerCase) {
          return propValue.toLowerCase();
      } else {
          return propValue;
      }
  }
docs: Get an element CSS property on the page
  Thanks to JavaScript Kit: http://www.javascriptkit.com/dhtmltutors/dhtmlcascade4.shtml
  
  @api private
  @method _getPropValue
  @param {Object} element
  @param {String} propName
  @returns Element's property value