body, html {
height:100%;
}

#container{
height:100%;
text-align: center;
}

#flash {
width: 808px;
height: 608px;
position:relative; /*allows for top property to move the element*/
top:50%; /*moves it 50% of #container's height down the page*/
margin-top:-304px; /*pulls it back up by half it's height*/
margin-left: auto;margin-right: auto; /*H-centering in complaint browsers*/
}