console 命令行工具 X clear
console
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8"> 
<title>菜鸟教程(runoob.com)</title>
<style> 
  *{
      margin: 0;
      padding: 0
  }
  ul{
      list-style: none
  }
  .box{
     display: flex;
     width: 500px;
     height: 400px;
     flex-wrap: wrap;
     justify-content: space-around;
     align-content: space-around;
     border: 1px solid #ccc
  }
  .box li{
      /* flex: 1; */
      width: 150px;
      height: 150px;
      border: 1px solid red;
  }
</style>
</head>
<body>

<div id="main">
    <ul class="box">
        <li></li>
        <li></li>
        <li></li>
        <li></li>
        <li></li>
        <li></li>
    </ul>
</div>



</body>
</html>