jQuery遮罩弹窗

HTML:

<p id="ok">单击这里显示</p>

JS:

$(document).ready(function(){
    $("#ok").click(function(){
        showBg();
        addBox();
    });
});
function showBg(){
    var _body = $("body").eq(0);
    $("html,body").css("overflow","hidden");
    if($("#bg").length == 0){
        _body.append("<div id=\"bg\"><iframe src=\"\" width=\"100%\" height=\"100%\" frameBorder=\"0\"></iframe></div>");
        $("#bg").css({"background-color":"#000000","opacity":".5","filter":"alpha(opacity=50);","z-index":"100","position":"absolute","top":"0","width":_body.width(),"height":_body.height()});
        $("#bg iframe").css({"opacity":"0","filter":"alpha(opacity=0);"});
    }else{
        $("#bg").show();
    }
}
function hiddenBg(){
    $("html,body").css("overflow","auto");
    $("#bg").hide();
    $("#dialog").hide();
}
function addBox(){
    var _body = $("body").eq(0);
    if($("#close").length == 0){
        _body.append("<div id=\"dialog\"><span id=\"close\" style=\"float:right;cursor:pointer;border:#333 solid 1px;\">×</span></div>");
        $("#dialog").css({500,height:200,position:"absolute","z-index":"101",top:(_body.height() / 2 - 100),left:(_body.width() / 2 - 250),"background-color":"#ffffff"});
        $("#close").click(function(){
            hiddenBg();
        });
    }else{
        $("#dialog").show();
    }
}