flex布局第一行div左對齊，第二行中對齊，第三行右對齊

.flex{

      display:flex;

      flex-direction:column;

      width:600px;

  }

.flex div{

      width:100px;

      height:100px;

      background:red;

      margin-left:2px;

  }

.flex div:nth-of-type(1){

      align-self:flex-start;

  }

.flex div:nth-of-type(2){

     align-self:center;

  }

.flex div:nth-of-type(3){

     align-self:flex-end;

  }