code: public void drawStartRectangle(Double width) {
  		GraphicsContext vectorContext = mapWidget.getVectorContext();
  		vectorContext.drawRectangle(group, MAP_AREA, 
  				applyMargins(new Bbox(0, 0, width, getHeight())), 
  				// IE9 does not draw an empty shapestyle (new ShapeStyle()), but it does draw one with opacity = 0...
  				new ShapeStyle("#FF0000", 0, "#FF0000", 0, 1)); 
  //				new ShapeStyle("#FF0000", 0.1f, "#FF0000", 0.5f, 1));
  		vectorContext.setCursor(group, MAP_AREA, Cursor.POINTER.getValue());
  	}
docs: Provides a rectangle over the area over which the user can slide.
  An onDown event redraws this rectangle into one that covers the map with {@link SliderArea#drawMapRectangle()}.