#BlockWindow
{
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    opacity: .5;
    background-color: #000;
    z-index: 10000;
}
#BlockWindow div
{
    position: absolute;
    top: 50%;
    left: 50%;
    width: 5em;
    height: 2em;
    margin: -1em 0 0 -2.5em;
    color: #fff;
    font-weight: bold;
}