function initMenu() {
    $$('#sidebar h3 a').each(function(el){
        el.observe('mouseover', function(e){
            var item = Event.element(e);
            item.setStyle({fontSize: '18px'});
        });
        el.observe('mouseout', function(e){
            var item = Event.element(e);
            item.setStyle({fontSize: '15px'});
        })
    })
}

Event.observe(window, 'load', initMenu);