.gwt-DialogBox .Caption {
  position: relative;  
}
.gwt-DialogBox .dialogControls { 
  position: absolute;
  top: 6px;
  right: 6px;
}
.gwt-DialogBox .dialogControls a {
  cursor: pointer;
}
.gwt-DialogBox .dialogControls .x {
  display: block;
  height: 13px;
  width: 13px;  
  background: transparent url(x.png) center center no-repeat;
  -background: transparent url(x.gif) center center no-repeat;
}