code: public void setSliderPosition(float x, float y) {
  
          if (x > 255) {
              x = 255;
          }
          if (x < 0) {
              x = 0;
          }
          if (y > 255) {
              y = 255;
          }
          if (y < 0) {
              y = 0;
          }
          x -= 7;
          y -= 7;
          m_slider.getElement().getStyle().setLeft(x, Unit.PX);
          m_slider.getElement().getStyle().setTop(y, Unit.PX);
      }
docs: Sets the slider's position along the x-axis and y-axis.<p>
  @param x position along the x-axis [0-256]
  @param y position along the y-axis [0-256]