jQuery CSS implements menu sliding expansion and contraction (imitation of Taobao)_jquery

body,div,dl,dt,dd,ul,ol,li,h1,h2,h3,h4,h5,h6,br,pre,form,fieldset,input,textarea,p,blockquote,th,td{
margin:0;
padding:0
}
span{
color:#FF2B13
}
a{
text-decoration:none;
color :#515050
}
a:hover{
text-decoration:underline;
color:red
}
.box_all{
overflow:hidden;
width :350px;
font-family:"Microsoft Yahei";
font-size:14px;
border:1px solid #EEEEEE;
border-top:2px solid #F57A04;
padding:0 0 10px 0;
margin:0 auto
}
.box{
padding-left:45px;
padding-top:5px
}
.box li{
line-height:20px;
margin-right:30px;
width:120px;
text-align:left;
float:left;
list-style- type:none
}
.boxdown{
cursor:pointer;
border:1px solid #EEEEEE;
width:60px;
height:14px;
background:# FFFFFF url(../images/down.png) no-repeat 20px;
margin-left:150px;
margin-top:-2px;
border-top:none;
margin: 0 auto
}
.up{
cursor:pointer;
border:1px solid #EEEEEE;
width:60px;
height:14px;
background:#FFFFFF url(../images/up.png) no-repeat 20px;
margin-left:150px;
margin-top:-2px;
border-top:none;
margin:0 auto
}

$(document).ready(function(){
var a =$(".box ul li:gt(3):not(:last)");
a. hide();
$(".boxdown").click(function(){
if(a.is(':visible')){
a.slideUp('fast');
$(this).removeClass('up');
}else{
a.slideDown('fast').show();
$(this).addClass('up') ;
}
});
});