在css嵌套中的html的table里的字左右不对齐

【现象】AAAA与天数的数字左右不居中

<table border=1 align="center">
<tr>
<td width="20%" align="center">AAAA</th>
<td width="10%" align="center">周一→周二</th>
<td width="10%" align="center">周二→周三</th>
<td width="10%" align="center">周三→周四</th>
<td width="10%" align="center">周四→周五</th>
<td width="10%" align="center">周五→周一</th>
</tr>

<tr>
<td width="20%" align="center">天数</td>
<td width="10%" align="center">1</td>
<td width="10%" align="center">1</td>
<td width="10%" align="center">3</td>
<td width="10%" align="center">1</td>
<td width="10%" align="center">1</td>
</tr>
</table>

【解决方法】

<table border=1 align="center">
<tr>
<td width="20%" align="center" style="vertical-align:middle;">XXXX</th>
<td width="10%" align="center">周一→周二</th>
<td width="10%" align="center">周二→周三</th>
<td width="10%" align="center">周三→周四</th>
<td width="10%" align="center">周四→周五</th>
<td width="10%" align="center">周五→周一</th>
</tr>

<tr>
<td width="20%" align="center">XXXXXXX天数</td>
<td width="10%" align="center" style="vertical-align:middle;">1</td>
<td width="10%" align="center" style="vertical-align:middle;">1</td>
<td width="10%" align="center" style="vertical-align:middle;">3</td>
<td width="10%" align="center" style="vertical-align:middle;">1</td>
<td width="10%" align="center" style="vertical-align:middle;">1</td>
</tr>
</table>

参考

http://www.webhek.com/vertical-align/