cant add custom css

If I select custom css and add code like below nothing happensz
Checking the database I can see it never gets written to the table that holds that value. Is there something Im doing wrong? I’m trying to add a background image to the login page that is a little better than the default white page.

body
 {
 background-image:url('http://url.to.add/background//password-protector-background.jpg');
 background-repeat:no-repeat;
 background-position:center;
 }

Thanks!

http://ww.wp.xz.cn/extend/plugins/password-protect-wordpress/