display:flex属性 justify-content: space-between和flex-flow:wrap一起使用的问题

.wrap {
    width: 400px;
    display:flex;  /*弹性盒子*/
    justify-content: space-between;  /*两端对齐，子元素之间有间隙*/
    flex-flow: row wrap;/*子元素溢出父容器时换行*/
}
span {width: 100px;background-color: green;color:#fff;border-radius: 5px;margin-top: 10px;padding: 10px;}
           

<div class="wrap">
    <span>11</span>
    <span>22</span>
    <span>33</span>
    <span>44</span>
    <span>55</span>
</div>
           

 解决方法：追加一个空的子元素

.wrap:after {content: ""; width: 120px; }