表格的css 怎么修改

[weixin_38119488]

<table border="1" style="width:100%">

<tr>
<td>aaaaaa</td>
<td>aaaaaa</td>
<td>aaaaaa</td>
<td>aaaaaa</td>
</tr>
<tr>
<td>aaaaaa</td>
<td>aaaaaa</td>
<td>aaaaaa</td>
<td>aaaaaa</td>
</tr>
<tr>
<td>aaaaaa</td>
<td>aaaaaa</td>
<td>aaaaaa</td>
<td>aaaaaa</td>
</tr>

</table>

怎么把一个<table>的样式变成如下图的？？？？ 
就是把第二行的最后一格拉宽，
 本人菜鸟一个，请求大神帮助