function sipka(id){
var text;

document.getElementById(id).style.backgroundImage='url("img/menu_hover.jpg")'; 
} 

function sipka2(id){
var text;

document.getElementById(id).style.backgroundImage='url("img/menu.jpg")'; 
} 

function button1(id){
var text;

document.getElementById(id).style.backgroundImage='url("img/box_button_hover.jpg")'; 
} 

function button2(id){
var text;

document.getElementById(id).style.backgroundImage='url("img/box_button.jpg")'; 
}
function show(id){
document.getElementById('menul' + id).style.visibility='visible';
document.getElementById('menup' + id).style.visibility='visible';
document.getElementById('center' + id).style.backgroundImage='url("img/list-back.jpg")';
}

function hidden(id){
document.getElementById('menul' + id).style.visibility='hidden';
document.getElementById('menup' + id).style.visibility='hidden';
document.getElementById('center' + id).style.backgroundImage='none';
}