html怎么做到这样？告诉一下

img

实现如下，请采纳谢谢。

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>test</title>
    <style>
        .box{
            height: 100px;
            width: 100px;
            border:1px solid #666;
            margin-bottom:10px;
            box-sizing:border-box;
        }
        .inner {
            height:50px;
            width:50px;
            background:yellow;
            border:none;
            box-sizing:border-box;
        }
    </style>
</head>
<body>
     <div class="box"></div>
     <div class="box">
        <div class="inner"></div>
     </div>
</body>
</html>