z-index is not working for slider in the ajaxtabcontainer

<div><div id="simplegallery2" style="  width:202px;height:160px; display:block;z-index:-1;"></div></div>    

    <script type="text/javascript" src="Banner/js/jquery.min.js"></script>
    <script type="text/javascript" src="Banner/js/simplegallery.js"></script>
    
      <script type="text/javascript">
          var mygallery2 = new simpleGallery({
              wrapperid: "simplegallery2",
              dimensions: [202, 160],
              imagearray: [

                  ["Images/Division/CircularMagnet/lmr_x.png"],
                  ["Images/Division/CircularMagnet/lmr1_x.png"]
              

              ],
              autoplay: [true, 2500, 100],
              persist: true,
              fadeduration: 2000,
              oninit: function () {
              },
              onslide: function (curslide, i) {

              }
          })

</script>