div居中的另类做法

<div style="height:25%"></div>
<div style="text-align:center;vertical-align:middle;line-height:300px;">
<table>
<tr>
<td colspan="3" align="center"><img src="img/login.png"/></td></tr>
<tr>
<td>user:<input type="text" name="user"/></td>
<td>password:<input type="password" name="password"/></td>
<td><input type="submit" name="login" value="login"/></td>
</tr>
</table>
</form>
</div>