[Deff]

<style type="text/css">
.wrap {
  left:0;
  top:0;
  margin:0;
  padding:0;
  width:100%;
  height:100%;
  position:fixed;
  background-color:rgba(0,0,0,.8);
  color:#fff;
}
div.cnt {
  position:absolute;
  top: 0; left: 0; bottom: 0; right: 0;
  margin:auto;
  width:200px;
  height:100px;
  border: solid 1px;
}
</style>
<img src="http://javascript.ru/forum/images/smilies/smile.gif" width=30%>

 <div class=wrap>
 <div class=cnt></div>
</div>