function showModalDiv(maskDiv, modalDiv) {
    //show mask div
    var maskDiv = document.getElementById(maskDiv);
    maskDiv.style.display = "inline";
    
    //fade modal in
    $('#' + modalDiv).fadeIn(1000);
}
function hideModalDiv(maskDiv, modalDiv) {
    //fade modal out
    $('#' + modalDiv).fadeOut(1000);
    
    //hide mask afterwards
    var maskDiv = document.getElementById(maskDiv);
    setTimeout(function() { maskDiv.style.display = "none"; }, 1000);
}