CSS Kayma Sorunu!

#post{
background-color:#FFF;
box-shadow: 0px 0px 6px #000000; /* Standart */
-moz-box-shadow: 0px 0px 6px #000000; /* Firefox */
-webkit-box-shadow: 0px 0px 6px #000000; /* Safari ve Chrome */
border-radius:3px;
-moz-border-radius:3px; /* Firefox */
-webkit-border-radius:3px; /* Safari ve Chrome */
overflow:hidden;
width:971px;
/*ort-kon*/
margin-top:-21px;
margin-left:auto;
margin-right:auto;
/*pad*/
padding-top:36px;
padding-left:15px;
padding-bottom:10px;
/*index*/
position:relative;
z-index:-1;
}