：hover

1、鼠标移动到div上，改变div的样式

div：hover{
    background-color:red;
}

<div>aaaaaaa</div>

2、使用hover显示隐藏的模块

<span class="order-details-text">
    <span class="order-details" >
    　　详细
       <span class="triangle_border_down"></span>
    </span>
    <span class="your-order">
    　　<ul class="your-order-list ">
       　　<li class="list-order-num">150150766970515</li>
          <li class="list-order-num">150150766970511</li>
          <li class="list-order-num">150150766970525</li>
       </ul>
    </span>
</span>

.order-details-text:hover .your-order-list{
    display: block;
}

注意：用hover显示隐藏的模块，该隐藏的模块必须是鼠标滑动到的模块的子模块，如要显示your-order-list，鼠标滑动到模块order-details-text，那么your-order-list必须是order-details-text的子元素