// this function puts the dark screen over the entire page
function DarkenPage()
{
    var page_screen = document.getElementById('page_screen');
    //page_screen.style.height = document.body.parentNode.scrollHeight + 'px';
    page_screen.style.display = 'block';
}

// this function removes the dark screen and the page is light again
function LightenPage()
{
    var page_screen = document.getElementById('page_screen');
    page_screen.style.display = 'none';
}