解决flex布局中 space-between 最后一行元素的排版问题

 当child元素最后一行不为3个时，这样写会导致最后一行的元素垂直方向上不与之前的行元素对齐

parent {
    width: 300px;
    display: flex;
    flex-direction: row;
    flex-wrap: wrap;
    justify-content: space-between;
}

child {
    width: 100px;
    height: 50px;
}

 只需要在parent加一个CSS伪类即可解决

parent {
    width: 300px;
    display: flex;
    flex-direction: row;
    flex-wrap: wrap;
    justify-content: space-between;

    &::after {
      content: '';
      flex: auto;
    }
}