<div id="parent">
  <div id="first">One</div>
  <div id="second">Second</div>
  <div id="three">Three</div>
  <div id="last">Last</div>
</div>

#parent {
  display: flex;
  flex-direction: column;
  height: 50vh;
}

#second, #three {
  margin-top: 20px;
}

#last {
  marging-top: auto;
}