跟着老师做的为什么会这样？

css

.index-pics {
   height: 382px;
   overflow: hidden;
}
.index-pics .pic-col{
   float: left;
}
.index-pics .pic-col-m{
   width: 353px;
}
.index-pics .pic-col-s{
   width: 287px;
}
.index-pics .pic-col-l{
   width: 460px;
}

index

<div class="index-panel-body index-pics"></div>
   <a class="pic-col pic-col-m"><img src="images/demo6.jpg" alt=""/></a>
   <div class="pic-col pic-col-s">
       <a class="pic-row"><img src="images/demo7.jpg" alt=""/></a>
       <a class="pic-row"><img src="images/demo8.jpg" alt=""/></a>
   </div>
   <a class="pic-col pic-col-l"><img src="images/demo9.jpg" alt=""/></a>
</div>