* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

.box {
  margin: 10px auto;
  outline: 1px solid red;
  width: 600px;
  overflow: auto;
}

.box div {
  overflow: hidden;
}

.box p {
  width: 200px;
  height: 100px;
  border: 2px solid #000;
  margin: 0 auto;
}

.box.num3 p {
  float: left;
}
.box.nums div{
  width: 800px;
}
.box.nums div p{
  float: left;
}