MyClassName {
  display: flex;
  flex-direction: column;
  align-items: center;
}

Centering multiple div sections as columns or vertically for mobile

CSS

.my_container {
  display: flex;
  flex-direction: column;
  align-items: center; /*or flex-start for top aligned */
  justify-content: center;
  gap: 20px; /* spacing between items */
  margin: 20px 0;
}

.my_section {
  width: 100%;
  max-width: 400px;
}

@media only screen and (max-width: 768px)
{
  .my_container
  {
    flex-direction: row;
    flex-wrap: wrap;
  }

  .create_proof_option_section
  {
    width: auto;
  }
}

HTML

  <div class="my_container">
    <div class="my_section">

    </div>

    <div class="my_section">
    
    </div>

    <div class="my_section">
    
    </div>
  </div>