SOURCE

<h3>上下边距折叠</h3>
<div class="box box1">内容区</div>
<div class="box box2">内容区</div>


<div class=" box3">
  <div class="box4">内容区</div>
</div>

<div class="box5"></div>

.box {
  width: 80px;
  height: 60px;
  background: #bbb;
  border: 2px solid black;
  padding: 10px;
}

.box1 {
  margin-bottom: 30px;
}

.box2 {
  margin-top: 20px;
}

.box3 {
  margin-top: 50px;
  border:none;
  padding:none;
  background: #bbb;
  width: 80px;
}

.box4 {
  margin-top: 20px;
}

.box5 {
  margin-top: 20px;
  margin-bottom: 20px
}