How to move login box

Hi there,

I’ve tried changing the position of the login form but the code doesn’t seem to work.
This is my login page: http://www.gwynnegraphics.com/login/
This is the code:
.login form {
margin-top: 200px;
}

Where am I going wrong? I just want the login box moved down to the middle of the screen. I don’t want a logo on there you see.

Thanks