Table实现表头固定 内容滚动

<div style="width: 800px;">
    <div class="table-head">
    <table>
        <colgroup>
            <col style="width: 80px;" />
            <col />
        </colgroup>
        <thead>
            <tr><th>序号</th><th>内容</th></tr>
        </thead>
    </table>
    </div>
    <div class="table-body">
    <table>
        <colgroup><col style="width: 80px;" /><col /></colgroup>
        <tbody>
            <tr><td>1</td><td>我只是用来测试的</td></tr>
            <tr><td>2</td><td>我只是用来测试的</td></tr>
            <tr><td>3</td><td>我只是用来测试的</td></tr>
            <tr><td>4</td><td>我只是用来测试的</td></tr>
            
        </tbody>
    </table>
    </div>
</div>

.table-head{padding-right:17px;background-color:#999;color:#000;}
.table-body{width:100%; height:300px;overflow-y:scroll;}
.table-head table,.table-body table{width:100%;}
.table-body table tr:nth-child(2n+1){background-color:#f2f2f2;}