jquery实现按钮翻转动画

<div id="login_btn">
  <button onclick="login()"><img src="../../App_Themes/page/images/login_btn.png" alt="登录" title="登录" /></button>
</div>

#login_btn { margin-left:78px; margin-top:10px; background:url("./images/login_btn.png") left bottom no-repeat; width:184px; height:39px; overflow:hidden;}
#login_btn button {border:none; background:url("./images/login_btn.png") left top; cursor:pointer;}
#login_btn span {display:block; width:100%; height:100%; cursor:pointer;}

          // 登录按钮特效
          function Login_btn() {
            $(‘#login_btn‘).prepend(‘<span></span>‘);
            $(‘#login_btn‘).hover(function() {
              $(this).find(‘span‘).stop().animate({marginTop:"-39px"},250);
            },function() {
              $(this).find(‘span‘).stop().animate({marginTop:"0"},250);
            })
          }