                        课程
                    
                        /前端开发
                        
                            /jQuery
                        
                        /jQuery基础课程

求问代码为什么不能实现？

<!DOCTYPE html>
<html>
    <head>
        <title>使用$.extend()扩展工具函数</title>
       <script src="http://libs.baidu.com/jquery/1.9.0/jquery.js" type="text/javascript"></script>
        <style>
            *{
                margin:0;padding:0;
                }
            div{
                width:300px;
                margin:10px auto;
                padding:5px;
                }
            span{
                margin:10px;
            }
            li{
                list-style:none;
                margin:10px auto;
                width:100px;
                border:1px solid;
            }
        </style>
        
        <script>
           $(function () {
                $("li").each(function(index){
                    var a = $("#a").val();
                    $("li:eq(index)").hover(
                        function(){
                         $(this).css("background-color", "a");
                        },
                        function(){
                         $(this).css("background-color", "#fff");
                        })
                })
            }); 
            
        </script>
    </head>
    
    <body>
    <div>
        <span>输入颜色:</span><input type="text" id="a" >
        <ul>
            <li>1</li>
            <li>22</li>
            <li>333</li>
            <li>4444</li>
            <li>55555</li>
        </ul>
        <div id="content"></div>
    </div> 
    </body>
</html>

求问哪里错了？