jquery实现下拉菜单的手风琴效果

<div class="site-nav">
 <ul class="site-accordion">
 <li>
 <div class="tab-head">学科领域</div>
 <ul class="tabs-list">
 <li>机械电子</li>
 <li>生物工程</li>
 <li>能源环保</li>
 <li>化学化工</li>
 </ul>
 </li>
 <li>
 <div class="tab-head">省份地区</div>
 <ul class="tabs-list">
 <li>陕西省</li>
 <li>江苏省</li>
 <li>山东省</li>
 <li>河南省</li>
 </ul>
 </li>
 <li>
 <div class="tab-head">经费范围</div>
 <ul class="tabs-list">
 <li>50万~100万</li>
 <li>100万~200万</li>
 <li>200万~500万</li>
 <li>500万以上</li>
 </ul>
 </li>
 <li>
 <div class="tab-head">需求状态</div>
 <ul class="tabs-list">
 <li>状态1</li>
 <li>状态2</li>

 </ul>
 </li>

 </ul>
</div>

.site-accordion>li{
 margin-top: 13px;
}
.site-accordion>li .tab-head{
 width: 160px;
 height: 40px;
 line-height: 40px;
 text-align: center;
 color: #9c9c9c;
 font-size: 16px;
 background: #f2f2f2;
}
.site-accordion>li .tab-head:hover{
 background: #292d48;
}
.site-accordion>li .tab-head:after{
 content: '';
 border: 5px solid #4F5160;
 border-color: #4F5160 transparent transparent transparent;
 margin-top: 20px;
 position: relative;
 top: 10px;
 left: 5px;
}
.site-accordion>li .tabs-list{
 display: none;
}
.site-accordion>li .tabs-list li{
 width: 160px;
 height: 40px;
 line-height: 40px;
 text-align: center;
 color: #9c9c9c;
.site-accordion>li .tabs-list li:hover{
 background: #f2f2f2;
} 

$('.tab-head').click(function(){
 $(this).next().slideToggle();
 $('.tab-head').css('background','#FFFFFF');
 $(this).css('background','#292d48');

 })