*{margin:0;padding:0;}
.box{
  margin:10px 0;
  display: flex;
  flex-wrap: wrap;
  border:1px solid red;				
}
p{
  height:100px;
  border:1px solid #ccc;
  line-height: 100px;
  text-align: center;
  flex:auto;
  width: 20%;
}