jquery 登录窗口--www.
   
        body
        {
            margin:0px;
            padding:0px;   
        }
        #shadow
        {
            width:100%;
            height:100%;
            opacity:0.2;
            filter:alpha(opacity=20);
            background-color:gray;
            z-index:0;
            position:absolute;
            left:0px;
            top:0px;
            display:none;
        }                   
        #login{width:220px;border:1px solid red;display:none;position:absolute; }           
   
   
   
        var $shadow;
        var $login;
        $(function () {
            $shadow = $("#shadow");
            $login = $("#login");

            $("#btnshow").click(function () {
                $shadow.show();
                var leftpx = ($shadow.width() - $login.width()) / 2 + "px";
                var toppx = ($shadow.height() - $login.height()) / 2 + "px";
                $login.css({ "left": leftpx, "top": toppx });
                $login.slidedown(2000);
            });
            $("#btncancel").click(function () {
                $login.slideup(3000, function () {
                    $shadow.hide();
                });
            });
        });