[Deff]

<style>
#foo{
  position:fixed;
  left:50%;
  margin-left:-100px;
  top:12%;
  height:100px;
  width:200px;
  background-color:#F8F8F8;
  border:outset 2px;
  transition-property:top;
  -webkit-transition-property:top;
  -moz-transition-property:top;
  -o-transition-property:top;
  -ms-transition-property:top;

   transition-duration: 0.96s;
  -webkit-transition-duration: 0.96s;
  -moz-transition-duration: 0.96s;
  -o-transition-duration: 0.96s;
  -ms-transition-duration: 0.96s; /* IE9+ */
}

</style>
<div id=foo>блаблаблабла блаблаблаблаблаблаблабла я див</div>
<script type="text/javascript">
document.write('<style>#foo{top:45%}</style>')
</script>