Why doesn't align-self work in Bootstrap 4?

Question

Bootstrap

It does not work for me align-selfwhen using Bootstrap 4. It seems that I specified everything correctly, but it does not work. Where is the mistake?

//Хотел сделать кнопки в виде ступенек
<div class="border border-info flex-container" style="height: 8rem;">
<div class="d-flex justify-content-between">
  <div class="d-flex align-self-start">
    <button class="btn btn-outline-success">Qwerty</button>
   </div> 
  <div class="d-flex align-self-center">
    <button class="btn btn-outline-success">Qwerty</button>
  </div>	
  <div class="d-flex align-self-end">
  <button class="btn btn-outline-success">Qwerty</button>
  </div>
</div>
</div>

Answer 1

Set this height: 8rem to Either style the d-flex justify-content-between
<div class="d-flex justify-content-between">

.d-flex.justify-content-between {
    height: 100%;
}