#test{border-collapse:collapse;border:1px solid #ddd;}
#test th,#test td{border:1px solid #ddd;}
<table id="test">
<tr><th>姓名</th><td>少年</td></tr>
<tr><th>年龄</th><td>20</td></tr>
</table>
#test{border-collapse:collapse;border:1px solid #ddd;}
#test th,#test td{border:1px solid #ddd;}
<table id="test">
<tr><th>姓名</th><td>少年</td></tr>
<tr><th>年龄</th><td>20</td></tr>
</table>