How to set left and top positions of alert box using JQuery in the below code?

<script>
$(document).ready(function() {
    if(document.getElementById("faxNoId").value=="- -"){
        var show=document.getElementById("add");
        var hide=document.getElementById("edit");
        show.style.display = "inline";
        hide.style.display="none";
    }else{
        var customers=document.getElementById("faxNoId").value;
        var hide=document.getElementById("add");
        var show=document.getElementById("edit");
        show.style.display = "inline";
        hide.style.display="none";
    }
    document.getElementById("timer").style.display = "none";
    if(document.getElementById("faxNoId").value=="- -"){
        var cusno=$("#custNoId").val();
        $("#dialog-contactAlert").dialog({
            autoOpen: false,
            height: 300,
            width: 450,
            modal: true,
            open: function (event, ui) {
               $('#dialog-contactAlert').css('overflow', 'hidden');
               }
         });
        var dataString='<div><br>Customer Contact Details are incomplete, \n Do you want to update the details? <br><br><input type=button class=button value=Update name=theButton onclick=open_faxaddress('+cusno+') style=background-color: #888; color: #FFF;/> <input type=button value=Cancel class=button name=theButton1 onclick=open_close() style=background-color: #888; color: #FFF;/></div>';
         $('#dialog-contactAlert').html(dataString);
         $("#dialog-contactAlert").dialog("open");
    }
    });

    function open_faxaddress(cusno){
        open_faxadd(cusno);
        $("#dialog-contactAlert").dialog("close");
    }

    function open_close(){
        $("#dialog-contactAlert").dialog("close");
    }

</script>