帮我看看那里错了，怎么么有效果啊
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>jQuery动画特效</title>
<style>
div{width:100px;
height:100px;
background:red;
position:absolute;
}
</style>
<script>
$(function(){
$("#btn1").bind("click",function(){
$("div").animate({left:"+=50px"},300)
});
$("#btn2").bind("click",function(){
$("div").animate({left:"-=50px"},300)
});
})
</script>
</head>
<body>
<input id="btn1" type="button" value="向左"/>
<input id="btn2" type="button" value="向右"/>
<div></div>
</body>
</html>
