css盒子可控大小-resize

 <style>
        .father {
            padding: 20px;
            width: 200px;
            height: 50px;
            max-width: 800px;
            max-height: 800px;
            border: 1px solid #000;
            overflow: auto;
            resize: both;
        }

        .son {

            width: 50px;
            height: 20px;
            padding: 100px;
            background-color: aqua;
        }
    </style>
    <div class="father">
        <div class="son">1123</div>
    </div>