老师两个问题，第一个：我这个实现出来的效果为啥第三张图片显现不出来？第二个：我这个代码还能在简洁吗？

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <title></title>
  <style type="text/css">
    /*此处写代码*/
    *{margin:0;padding:0;
        font-family:"微软雅黑";
        color:#fff;
        margin:0 auto;
    }
    .head{width:100%;
        height:100px;
        background:#000 url(http://img1.sycdn.imooc.com/climg//58c0d2d900016ce303000100.png) no-repeat;
        line-height:100px;
        position:fixed;
    }
    .list1 li{
        margin-right:40px;
        list-style:none;
        display:inline-block;
        float:right;  
    }
    .content{
        width:100%;
        height:100%;
        padding-top:100px;
    }
    .con1{
        width:100%;
        height:480px;
        background:url(http://img1.sycdn.imooc.com/climg//58c0eda50001e12416000480.jpg) no-repeat;
    }
    .con2{ 
        width:100%;
        height:480px;
        background:url(http://img1.sycdn.imooc.com/climg//58c0edb80001c9f216000480.jpg) no-repeat;
    }
    .con3{
        width:100%;
        height:480px;
        background:url(http://img1.sycdn.imooc.com/climg//58c0edc9000100d516000480.jpg) no-repeat;
    }
    .foot{
        width:100%;
        height:100px;
        background:#000;
        text-align:center;
        position:fixed;
        bottom:0px;
    }
    .list2 li{
        list-style:none;
        display:inline-block;
       line-height: 100px;
       margin:0 15px;
    }
    </style>
</head>
<body>
  <!-- 此处写代码 -->
    <div class="container">
        <div class="head">
            <ul class="list1">
                <li>课程</li>
                <li>职业路径</li>
                <li>实践</li>
                <li>猿问</li>
                <li>手记</li>
            </ul>
        </div>
        <div class="content">
            <div class=con1></div>
            <div class="con2"></div>
            <div calss="con3"></div>
        </div>
        <div class="foot">
            <ul class="list2">
                <li>网站首页</li>
                <li>企业合作</li>
                <li>人才招聘</li>
                <li>联系我们</li>
                <li>常见问题</li>
                <li>友情链接</li>
            </ul>
        </div>
    </div>
</body>
</html>