body {
    text-align: center;
    background-color: lightblue;
    margin: 0;
    padding: 0;
}

#mainContainer {
    text-align: center;
    width: 600px;
    margin: auto;
}


#galleryContainer {
    display: none;
    
    position: absolute;
    top: 50px;
    left: 50px;
    width: 800px;
    height: 680px;
    
    border: 2px solid gray;}

#overlay {
    position: absolute;
    top: 0;
    left: 0;
    background-color: #000000;
    width: 100%;
    height: 100%;
    
    filter:alpha(opacity = 70);
    -moz-opacity: 0.7;
    opacity: 0.7;
    
    margin: 0;
    padding: 0;
}