Css thead 和 tbody 之间的间距

我有一个简单的html表，如下所示:

<table>
  <thead>
    <tr><th>Column 1</th><th>Column 2</th></tr>
  </thead>
  <tbody>
    <tr class="odd first-row"><td>Value 1</td><td>Value 2</td></tr>
    <tr class="even"><td>Value 3</td><td>Value 4</td></tr>
    <tr class="odd"><td>Value 5</td><td>Value 6</td></tr>
    <tr class="even last-row"><td>Value 7</td><td>Value 8</td></tr>
  </tbody>
</table>

我想用以下方式来表达:

• 带有方框阴影的标题行
• 标题行和第一个正文行之间的空格

我try 过不同的方法:

table {
    /* collapsed, because the bottom shadow on thead tr is hidden otherwise */
    border-collapse: collapse;
}
/* Shadow on the header row*/
thead tr   { box-shadow: 0 1px 10px #000000; }
/* Background colors defined on table cells */
th         { background-color: #ccc; }
tr.even td { background-color: yellow; }
tr.odd td  { background-color: orange; }

/* I would like spacing between thead tr and tr.first-row */

tr.first-row {
    /* This doesn't work because of border-collapse */
    /*border-top: 2em solid white;*/
}

tr.first-row td {
    /* This doesn't work because of border-collapse */
    /*border-top: 2em solid white;*/
    /* This doesn't work because of the td background-color */
    /*padding-top: 2em;*/
    /* Margin is not a valid property on table cells */
    /*margin-top: 2em;*/
}

另见:http://labcss.net/#8AVUF

有谁对我怎么做有什么建议吗？或者达到相同的视觉效果(即BOD-阴影+间距)？