.box{
          width:390px;
          height:500px;
          
          background:lightblue;
      }
      .box>li{
          float:left;
          margin-top:10px;
          width:120px;
          height:50px;
          margin-left:7px;
          
          background:skyblue;
          
          
          
          
      }
      .box>li>a{
          color:white;
          font-size:20px;
          line-height:50px;
          
          padding-left:10px;
          
      }
      
        
        
        .foot{
        
        margin:auto;
        
        font-size:12px;
        width:390px;
        height: 80px;
        line-height: 30px;
        text-align: center;
        color:grey;
      }
      .foot>p>img{
          position:absolute;
          top:608px;
          left:98px;
      }
      
      
     
  @media only screen and (max-width: 640px) {
  /*这里书写手机端的css代码，手机端的css代码是在pc端的代码基础上书写，类似于补充*/

      .box{
          width:390px;
          height:500px;
          
          background:lightblue;
      }
      .box>li{
          float:left;
          margin-top:10px;
          width:120px;
          height:50px;
          margin-left:7px;
          
          background:skyblue;
          
          
          
          
      }
      .box>li>a{
          color:white;
          font-size:20px;
          line-height:50px;
          
          padding-left:10px;
          
      }
      
      .foot{
        
        margin: auto;
        
        font-size:12px;
        width:390px;
        height: 80px;
        line-height: 30px;
        text-align: center;
        color:grey;
        background:lightgrey;
      }
      .foot>p>img{
          position:absolute;
          top:608px;
          left:98px;
      }
  }