function knopka (id) {
    document.getElementById(id).style.background = 'url(/javax.faces.resource/pols.jpg.xhtml?ln=images) repeat-x';
    document.getElementById(id).style.color = 'black';
    document.getElementById(id).style.width = '100%';
    document.getElementById(id).style.textAlign = 'center';
    document.getElementById(id).style.textShadow = 'grey 1px 1px 2px';
}