ExtJS textfield中添加图片

new Ext.form.TextField({
					fieldLabel:'用户名',
					name:'j_username',
					inputType:'text',
					width:250,
					allowBlank:false,
					cls : "login",
					style:{
						background: '#ffffff url(imgs/user.png) no-repeat left center',
						paddingLeft: '20px' 
					}, 
					blankText:'请输入'
					 
					
				}),
				
				new Ext.form.TextField({
					fieldLabel:'密码',
					name:'j_password',
					inputType:'password',
					width:250,
					allowBlank:false,
					style:{
						background: '#ffffff url(imgs/computer_key.png) no-repeat left center',
						paddingLeft: '20px' 
					}, 
					blankText:'请输入'