function showPopup(){
    setOverlayHeight();
    var overlay=document.getElementById('overlay');
    var popup=document.getElementById('popup');
    //attachEventListener(overlay, "mousedown", hidePopup, false);
    overlay.style.display='block';
    popup.style.display='block';
    DropDowns('');
   
}

function hidePopup(){
    DropDowns(1);
    var overlay = document.getElementById('overlay');
    var popup=document.getElementById('popup');
    overlay.style.display='';
    popup.style.display='';
}

function DropDowns(visibility){    
    var ddl=document.getElementsByTagName('select');
    for (var i=0; i<ddl.length; i++){
        if(visibility==''){
            ddl[i].style.visibility='hidden';
        }else{
            ddl[i].style.visibility='';
        }
    }
}

function setOverlayHeight(){
    var scrHeight=getScreenHeight();
    contentHeight=getElementsByClassName(document,'div','container')[0].offsetHeight;
    var overlay=document.getElementById('overlay');
    if(contentHeight>scrHeight){
        overlay.style.height=contentHeight+'px';
    }
}

function getScreenHeight(){
    scrHeight=0;
    if(typeof( window.innerWidth ) == 'number') {
        scrHeight = window.innerHeight;
    }else if( document.documentElement && ( document.documentElement.clientWidth || document.documentElement.clientHeight ) ) {
        scrHeight = document.documentElement.clientHeight;
    }else if( document.body && ( document.body.clientWidth || document.body.clientHeight ) ) {
        scrHeight = document.body.clientHeight;
    }
    return scrHeight;
}