Timeline 竖线

<div>

  <div class="left number">
    <span>1</span>
  </div>

  <div class="right content">
    <h3>Insert title</h3>
    <p>Insert description</p>
  </div>

</div>

%root% (div left number)::before{
  content: "";
  position: absolute;
  top: 65px;
  left: 50%;
  width: 1px;
  height: calc(100% - 75px);
  background-color: #ccc;
  transform: translateX(-50%);
}