function revealModal(divID) {
    window.onscroll = function() { document.getElementById(divID).style.top = document.body.scrollTop; };
    document.getElementById(divID).style.display = "block";
    document.getElementById(divID).style.top = document.body.scrollTop;
}

function hideModal(divID) {
    document.getElementById(divID).style.display = "none";
}