$(function(){
    $("#login_url").click(function(event){
       event.preventDefault();
       $("#login_form").dialog({
            modal: true,
            height: 200,
            width: 250,
            position: 'top',
            position: ['center', 200],
            overlay: {
                opacity: 0.6,
                background: "black"
            }
       });

       $("#login_form").show();
       $("#login_input").focus();
    });
});