window.onload = function() {
    var i, el, els = document.getElementsByTagName('span');
    for (i = 0; i < els.length; i++) {
        el = els.item(i);
        if (el.className == 'AspNet-Menu-NonLink' || el.className == 'AspNet-Menu-NonLink  AspNet-Menu-ChildSelected') {
            el.onclick = function() {
            this.parentNode.lastChild.style.backgroundColor = '#ffc';
            this.parentNode.lastChild.style.display = '';
            }
        };
    }
}