function mostra_contingut(seccio) {
    new Effect.Opacity('llcontingut', { from: 1, to: 0 , duration: 0.5});
    setTimeout("aux('"+seccio+"')",500);
}

function aux(seccio) {
    var o = document.getElementById('llcontingut');
    var c = document.getElementById(seccio);
    o.innerHTML = c.innerHTML;
    new Effect.Opacity('llcontingut', { from: 0, to: 1 , duration: 0.5});

}