Meine Lightbox funzt nicht mehr

<style type="text/css">
#makeItDark
{
position:absolute; top:0px; right:0px; left:0px; bottom:0px;
background-color:#000000;

/* For IE 5-7 */
filter: alpha(opacity=80);

/* For IE 8 */
-ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=80)";

/* For Safari >= 1.0 */
-khtml-opacity: 0.8;

/* For FireFox */
-moz-opacity: 0.8;

/* For all actual Browser with CSS 3*/
opacity: 0.8;

display:none;
}

#LightBox
{
background-color:#FDD017;
width:500px;
height:250px;
position:relative;
margin-left:auto; margin-right:auto;
text-align:center;
display:none;
}
</style>

<script type="text/javascript">
function LightBox()
{
var yposition = (window.innerHeight - 250) / 2;

if(document.getElementById('makeItDark').style.display == 'block')
{
document.getElementById('makeItDark').style.display = 'none';
document.getElementById('LightBox').style.display = 'none';
}
else
{
document.getElementById('makeItDark').style.display = 'block';
document.getElementById('LightBox').style.display = 'block';
document.getElementById('LightBox').style.top = yposition + 'px';
}
}
</script>

<input type="button" value="Lightbox" onclick="LightBox();" name="lightbut">
<div id="makeItDark">
<div id="LightBox">
Hallo ich bin eine Lightbox!
<input type="button" value="back" onclick="LightBox();" name="butreset">
</div>
</div>