code: public void setWidth(int width) {
  
          if (width <= 0) {
              m_containerElement.getStyle().clearWidth();
              m_width = -1;
          } else {
              m_containerElement.getStyle().setWidth(width, Unit.PX);
              m_width = width;
          }
      }
docs: Sets the width for the popup content.<p>
  
  @param width the width in pixels