function projects(){
document.getElementById('menu_bg').style.backgroundPosition = '0px -333px';
}

function articles(){
document.getElementById('menu_bg').style.backgroundPosition = '0px -666px';
}

function about(){
document.getElementById('menu_bg').style.backgroundPosition = '0px -1000px';
}

function contact(){
document.getElementById('menu_bg').style.backgroundPosition = '0px -1333px';
}

function rentals(){
document.getElementById('menu_bg').style.backgroundPosition = '0px -1667px';
}

function home(){
document.getElementById('menu_bg').style.backgroundPosition = '0px 0px';
}