<div class="ad" id="picBox">
        <div class="loading"><img src="images/loading.gif" alt="加载中..." /></div>
            <div class="pic">
                <li><a href="#"><img src="images/ad2.jpg" thumb="" alt="" text="详细描述2" /></a></li>
                <li><a href="#"><img src="images/ad3.jpg" thumb="" alt="" text="详细描述3" /></a></li>
                <li><a href="#"><img src="images/ad4.jpg" thumb="" alt="" text="详细描述4" /></a></li>
            </div>
   </div>
   <!-- 焦点结束 -->

.ad {
    overflow: hidden;
    height: 310px;
    
}

放加载图上一直显示加载图，没放也不显示焦点图