var IE = navigator.userAgent.indexOf('MSIE')!=-1;

function showhide( elemID ){
    var elem = document.getElementById( elemID );

    if(IE){
       var posY = document.documentElement.scrollTop+100;
    }else{
       var posY = window.pageYOffset+100;
    }

    if( elem.style.display == 'none' ){
		elem.style.display = 'block';
		elem.style.marginTop = posY+"px";
		document.getElementById('bg-popup').style.display = 'block';
    }else{
        elem.style.display = 'none';
		document.getElementById('bg-popup').style.display = 'none';
    }
}