ext使用Window弹出时实现关灯效果

function edit() {
var win;
if (!win) {
win = new Ext.Window({
//applyTo:'hello-win',
layout : 'auto',
//width : 800,
//height : 300,
autoHeight:true,
autoWidth:true,
closeAction : 'hide',
plain : true,
modal: true,
items : new Ext.FormPanel({
labelWidth: 75, // label settings here cascade unless overridden
url:'save-form.php',
frame:true,
title: '查看编辑',
bodyStyle:'padding:5px 5px 0',
width: 350,
defaults: {width: 100},
defaultType: 'textfield',