垂直中心绝对定位元素

Question

我正在尝试将table垂直居中li。我怎样才能做到这一点？以下是我到目前为止的情况：

<ul class="right_content>
    <li>
        <div class="content">
            <table class="table_class left_content">
                <tbody>
                    <tr>
                        <td style="padding:5px;>
                            <div class="content"> Stuff </div>
                        </td>
                    </tr>
                </tbody>
            </table>
        </div>
        <div>Some Stuff</div>
    </li>
    ...
</ul>


.right_content {
    position:fixed;
    right:0;
    top:55px;
    width:34px;
    list-style:none;
    margin:0;
    padding:0;
    z-index:1;
}

.right_content li {
    text-align:center;
    font-size:20px;
    position:relative;
    margin:0;
    padding:10px 0;
    line-height:20px;
    display:list-item;
    color:#999;
}

.content {
    position:relative;
    width:100%;
    height:100%;
}

.table_class {
    color:#fff;
    font-size:12px;
    background-color:#333;
    padding:10px;
}

.left_content {
    position:absolute;
    top:0;
    bottom:0;
    right:35px;
}