<div>
  <div class="box01">
    <div class="box-child">小さい箱</div>
  </div>
  <div class="box02">
    箱
  </div>
</div>

div{
  text-align: center;
}
.box01,.box02{
  width: 150px;
}
.box01{
  height:50px;
  margin-bottom: 20px;
  background-color: lightyellow;
}
.box-child{
  background-color: pink;
  margin-bottom: 30px;
}
.box02{
  margin-top: 30px;
  background-color: lightblue;
}