code: public static void setTransparency(Element elem, int alpha) {
  
          float ieVersion = getIEVersion();
          // only IE 8 requires special treatment, older IE versions are no longer supported
          if (ieVersion < 9.0) {
              elem.getStyle().setProperty(
                  "-ms-filter",
                  "\"progid:DXImageTransform.Microsoft.Alpha(opacity=" + alpha + ")\"");
          } else {
              // Everyone else
              elem.getStyle().setOpacity((1.0 * alpha) / 100);
          }
      }
docs: Given a DOM element, set the transparency value, with 100 being fully opaque and 0 being fully transparent.<p>
  
  @param elem A com.google.gwt.user.client.Element object
  @param alpha An alpha value