function abrir_ventana(){

var ventana=document.getElementById("ventana");

ventana.style.visibility='visible';

var pie=document.getElementById("pie").offsetTop;

ventana.style.height=pie+90;



}
function cerrar_ventana(){

var ventana=document.getElementById("ventana");
var vent_fondo=document.getElementById("vent_fondo");
ventana.style.visibility='hidden';
ventana.style.height=900;
vent_fondo.style.top=322;
}