function btnShow()
{
    var obj = document.getElementById("FloatDiv");
    obj.style.top = parseInt(document.documentElement.scrollTop) + 20 + 'px';
    setInterval("play()", 10); 

}
function play()
{
    var obj = document.getElementById("FloatDiv");
    obj.style.top = document.documentElement.scrollTop + parseInt(document.documentElement.clientHeight) - 20 + 'px';
}