#ui-blocker
{
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    opacity: .5;
    background-color: lightgray;
    z-index: 1000;
    overflow: auto;
}
    #ui-blocker div
    {
        position: absolute;
        top: 50%;
        left: 50%;
        width: 5em;
        height: 2em;
        margin: -1em 0 0 -2.5em;
        color: #fff;
        font-weight: bold;
    }
    
    #ui-blocker img 
    {
        display: block;
        margin-left: auto;
        margin-right: auto 
    }