每行的项目数固定，会自动分行。
.parent { width: 200px; height: 150px; background-color: black; display: flex; flex-flow: row wrap; align-content: flex-start; } .child { box-sizing: border-box; background-color: white; flex: 0 0 25%; height: 50px; border: 1px solid red; }
原文：https://www.cnblogs.com/jiunie/p/11341639.html