first = 1
last = 4
current = 1

function themesForward() {
	object = document.getElementById('themes' + current);
	new Effect.Fade(object, {duration: 0.3, queue: 'front'});
	
	if (current == last) { current = first; }
	else { current++ }
	object = document.getElementById('themes' + current);
	new Effect.Appear(object, {duration: 0.3, queue: 'end'});
}

function themesBack() {
	object = document.getElementById('themes' + current);
	new Effect.Fade(object, {duration: 0.3, queue: 'front'});
	
	if (current == first) { current = last; }
	else { current--; }
	object = document.getElementById('themes' + current);
	new Effect.Appear(object, {duration: 0.3, queue: 'end'});
}