没有实现导航项在水平方向居中显示，该改哪里

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style type="text/css">
    /*此处写代码*/
    .nav{
        background-color:black;
        width:1100px;
        height:100px;
        overflow: hidden;
        zoom:1;
        position:absolute;
        top:50%;
        left:50%;
        margin-top:-50px;
        margin-left:-550px;
    }
    .logo{
        text-align:left;
        float:left;
        cursor:pointer;
    }
    .column{
        width:60%;
        height:100px;
        color:white;
        font-size:20px;
        font-family:"微软雅黑"
        line-height:100px;
        float:right;
        text-align:right;
    }

    .column ul li{
        float:left;
        word-spacing:20px;
        list-style-type:none;
        margin:20px;
        cursor:pointer;
    }
</style>
</head>
<body>

<div class="nav">
     <div class="logo"><img src="http://img1.sycdn.imooc.com/climg//58c0d2d900016ce303000100.png"/></div>
     <div class="column">
         <ul>
             <li>课程</li>
             <li>职业路径</li>
             <li>实战</li>
             <li>猿问</li>
             <li>手记</li>
         </ul>
     </div>
</div>
</body>
</html>