div实现水平居中只需要设置固定宽度和margin:0 auto即可，
给你2个解决方案:
1、条件是div的高度和宽度是固定的
<style type="text/css">
<!--
div1 {
position:relative;
width:600px;
height:500px;
border:1px solid #008800;
}
div2 {
position:absolute;
top:50%;
left:50%;
margin:-150px 0 0 -200px;
width:400px;
height:300px;
border:1px solid #008800;
}-->
</style>
<div class="div1">
<div class="div2">让层垂直居中</div>
</div>
其实解决的思路是这样的：首们需要position:absolute;绝对定位。而层的定位点，使用外补丁margin负值的方法。负值的大小为层自身宽度高度除以二。
如：一个层宽度是400，高度是300。使用绝对定位距离上部与左部都设置成50%。而margin-top的值为－150。margin-left的值为－200。这样我们就实现了层垂直居中于父级层的样式编写。
2、条件是div的高度和宽度是不固定的
如果div宽度不固定，那用div就有点困难了，虽然用js获取当前高宽再附加css可以解决，但是要用到js来解决问题就有点逊了；
我给你一个思路，你不妨试试table布局，table不设置宽度的情况下默认是宽度和高度都是最小化的，这样给table设置margin:0 auto就可以让这个table水平方向居中；
解决了水平居中，那就来解决垂直居中，td中的内容默认是垂直居中的，那么只要两者互相嵌套一下不就解决水平垂直居中了!
但是有一个问题，你所需要垂直居中的父级table的高度是否固定，如果父级高度固定，那么子级高度不固定也一样可以垂直居中

让ecshop用户名、手机号、email登陆方法, 仅适用于没有做过任何平台整合的ECSHOP网站 修改文件： 1、includes/modules/integrates/ecshop.php $this->field_email = 'email'; 在以上代码下面增加 $this->field_phone = 'mobile_phone'; ===================================================================== 找到 function check_user($username, $password = null) 这个下面的 $sql = "SELECT " . $this->field_id . " FROM " . $this->table($this->user_table). " WHERE " . $this->field_name . "='" . $post_username . "'"; 修改为 $sql = "SELECT " . $this->field_id . " FROM " . $this->table($this->user_table). " WHERE " . $this->field_name . "='" . $post_username . "' or " . $this->field_phone . "='" . $post_username . "' or " . $this->field_email . "='" . $post_username . "'"; 再找到 $sql = "SELECT user_id, password, salt,ec_salt " . " FROM " . $this->table($this->user_table). " WHERE user_name='$post_username'"; 修改为 $sql = "SELECT user_id, password, salt,ec_salt " . " FROM " . $this->table($this->user_table). " WHERE user_name='$post_username' or mobile_phone='$post_username' or email='$post_username'"; 2、includes/modules/integrates/integrate.php 找到 /* 会员邮箱的字段名 */ var $field_email = ''; 在下面增加 /* 会员手机的字段名 */ var $field_phone = ''; 找到 function login($username, $password, $remember = null) 下面的 if ($this->need_sync) { $this->sync($username,$password); } 在上面增加 $sql = "SELECT " . $this->field_name . " FROM " . $this->table($this->user_table). " WHERE " . $this->field_phone . " = '$username' or " . $this->field_name . " = '$username' or " . $this->field_email . " = '$username'"; $username = $this->db->getOne($sql, true); 找到 function check_user($username, $password = null) 下面的 $sql = "SELECT " . $this->field_id . " FROM " . $this->table($this->user_table). " WHERE " . $this->field_name . "='" . $post_username . "'"; 修改为 $sql = "SELECT " . $this->field_id . " FROM " . $this->table($this->user_table). " WHERE " . $this->field_name . "='" . $post_username . "' or " . $this->field_phone . "='" . $post_username . "' or " . $this->field_email . "='" . $post_username . "'"; 找到 $sql = "SELECT " . $this->field_id . " FROM " . $this->table($this->user_table). " WHERE " . $this->field_name . "='" . $post_username . "' AND " . $this->field_pass . " ='" . $this->compile_password(array('password'=>$password)) . "'"; 修改为 $sql = "SELECT " . $this->field_id . " FROM " . $this->table($this->user_table). " WHERE (" . $this->field_name . "='" . $post_username . "' or " . $this->field_phone . "='" . $post_username . "' or " . $this->field_email . "='" . $post_username . "') AND " . $this->field_pass . " ='" . $this->compile_password(array('password'=>$password)) . "'"; 再找到 function sync ($username, $password='', $md5password='') 下面的 $sql = "SELECT user_name, email, password, sex, birthday". " FROM " . $GLOBALS['ecs']->table('users'). " WHERE user_name = '$username'"; 修改为 $sql = "SELECT user_name, email, password, sex, birthday". " FROM " . $GLOBALS['ecs']->table('users'). " WHERE user_name = '$username' or mobile_phone = '$username' or email = '$username'";

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http://www.douban.com/note/487300159/