Edit in JSFiddle

<div id="mydiv">
    http://bnson.blogspot.com/<br>
    http://bnson.blogspot.com/<br>
    http://bnson.blogspot.com/<br>
    http://bnson.blogspot.com/<br>
    http://bnson.blogspot.com/<br>
    http://bnson.blogspot.com/<br>
    http://bnson.blogspot.com/<br>
</div>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>
http://bnson.blogspot.com/<br>

#mydiv {
    top: 50%;
    left: 50%;
    width:26em;
    height:10em;
    margin-top: -5em; /*set to a negative number 1/2 of your height*/
    margin-left: -13em; /*set to a negative number 1/2 of your width*/
    border: 1px solid #ccc;
    background-color: #f3f3f3;
    position:fixed;
    text-align:center;
}