请帮忙看为什么不能实现背景颜色切换

Question

 <script>
          (function($){
              $.extend({
                 'focus':(function(){
                     $('li').mouseover(function(){
                         $(this).css('background-color','red');
                     
                   }); 
                 });
                 'blur':(function(){
                    $('li').mouseout(function(){
                         $(this).css('background-color','white'); 
                    });
                 });
              });
          })(jQuery);
          
          $(function(){
              $.focus();
              $.blur();
          })
      </script>