content：父元素
content-item: 子元素

主轴上子元素平均分布

.content {display: flex;flex-wrap: wrap;justify-content: space-between;.service-item {display: flex;flex-direction: column;justify-content: center;align-items: center;width: 80px;height: 80px;}
}

效果：

给父元素添加伪元素

.content:after {content: "";flex: auto;
}
.content {display: flex;flex-wrap: wrap;justify-content: space-between;.service-item {display: flex;flex-direction: column;justify-content: center;align-items: center;width: 80px;height: 80px;}
}

效果：