老师看一下有什么问题？

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style type="text/css">
        *{
            margin: 0;
            padding: 0;
            font: "microsoft yahei";
            font-size: 16px;
        }
        .page{
            background: url(./作业/mooc.png) no-repeat top center;
            width: 100%;
            height: 4000px;
        }
        .nav1{
            width: 160px;
            height: 205px;
            color: #FFF;
            font-size: 16px;
            text-align: center;
            position: fixed;
            top: 50%;
            margin-top: -102.5px;
            cursor: pointer;
        }
        .tit,.nav2 li,.nav3 div{
            width: 160px;
            height: 40px;
            line-height: 40px;
        }
        .list1{
            width: 160px;
            height: auto;
            background: #222;
            line-height: 40px;
            border-bottom: 1px #FFF solid;
        }
        .nav2{
            width: 160px;
            height: 123px;
            color: #222;
            display: none;
        }
        .nav2 li{
            background: #FFF;
            border-bottom: 1px #222 dashed; 
            position: relative;
        }
        .tit:hover{
            color: red;
        }
        .list1:hover .nav2{
            display: block;
        }
        .nav3{
            width: 160px;
            height: 123px;
            color: #FFF;
            
            position: absolute;
            left: 160px;
            top: 0;
            display: none;
        }
        .nav3 div{
            background: #222;
            border-bottom: 1px #FFF solid;
        }
        .nav2:hover .nav3{
            display: block;
        }
    </style>
</head>

<body>
    <div class="page">
        <div class="nav1">
            <div class="list1">
                <div class="tit">慕课网的标题信息</div>
                <ul class="nav2">
                    <li>
                        <div class="tit">二级栏目</div>
                        <div class="nav3">
                            <div class="tit">三级栏目</div>
                            <div class="tit">三级栏目</div>
                            <div class="tit">三级栏目</div>
                        </div>
                    </li>
                    <li class="tit">二级栏目</li>
                    <li class="tit">二级栏目</li>
                </ul>
            </div>
            <div class="list1">
                <div class="tit">慕课网的标题信息</div>
                <ul class="nav2">
                    <li class="tit">二级栏目</li>
                    <li class="tit">二级栏目</li>
                    <li class="tit">二级栏目</li>
                </ul>
            </div>
            <div class="list1">
                <div class="tit">慕课网的标题信息</div>
                <ul class="nav2">
                    <li class="tit">二级栏目</li>
                    <li class="tit">二级栏目</li>
                    <li class="tit">二级栏目</li>
                </ul>
            </div>
            <div class="list1">
                <div class="tit">慕课网的标题信息</div>
                <ul class="nav2">
                    <li class="tit">二级栏目</li>
                    <li class="tit">二级栏目</li>
                    <li class="tit">二级栏目</li>
                </ul>
            </div>
            <div class="list1">
                <div class="tit">慕课网的标题信息</div>
                <ul class="nav2">
                    <li class="tit">二级栏目</li>
                    <li class="tit">二级栏目</li>
                    <li class="tit">二级栏目</li>
                </ul>
            </div>
        </div>
    </div>    
</body>
</html>

雨之赞歌 2018-12-28

源自：CSS定位（弃用） 1-1 课程简介