// html結構
<div class="box">
    <div class="boxItem">
        <p style="height:300px;">第一級1111</p>
        <p style="height:500px;">第一級2222</p>
        <p>第一級3333</p>
    </div>
</div>

// css 樣式
.box{
        width: 280px;
        height: 600px;
        position: absolute;
        top: 33
 
px;
        left: 13px;
        /*cursor: pointer;*/
        overflow:hidden;
    }
    .boxItem{
        overflow-x: hidden;
        overflow-y: auto;
        color: #000;
        font-size: 14px;
        font-family: "\5FAE\8F6F\96C5\9ED1",Helvetica,"黑體",Arial,Tahoma;
        height: 100%;
    }
    /*滾動條樣式*/
 

    .boxItem::-webkit-scrollbar {/*滾動條整體樣式*/
        width: 4px;     /*高寬分別對應橫豎滾動條的尺寸*/
        height: 4px;
    }
    .boxItem::-webkit-scrollbar-thumb {/*滾動條裡面小方塊*/
        border-radius: 5px;
        -webkit-box-shadow: inset 0 0 5px rgba(0,0,0,0.2);
        background: rgba(0,0,0,0.2);
    }
    .boxItem::-webkit-scrollbar-track {/*滾動條裡面軌道*/
 

        -webkit-box-shadow: inset 0 0 5px rgba(0,0,0,0.2);
        border-radius: 0;
        background: rgba(0,0,0,0.1);
    }