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');

        })