spacearound 第二行居左

  .knowledgeContent{      父

    display: flex;
    flex-wrap: wrap;
    justify-content: space-around;
    /*align-items: start;*/
  }
  /*.knowledgeContent:after{*/
  /*  content:'';*/
  /*  width:347px;*/
  /*  height:0;*/
  /*  display:block;*/
  /*}*/
  .knowledgeContent:after {  父的伪类
    content: "";
    flex: auto;
    width:347px;
    display: block;
  }