you are missing a position: relative inside your slider, and then you can adjust the slider a span to have top:0 instead of top:11 and it will fix it for you.
#slider {
border: 1px solid #999999;
display: none;
position: relative;
}
#slider a span {
background-color: #999999;
color: #FFFFFF;
display: block;
height: 40px;
opacity: 0.4;
position: absolute;
top: 0px;
width: 558px;
}