bootstrap 4 change column order on mobile code example

Example 1: ordering collumns in bootstrap

<div class="container">
  <div class="row">
    <div class="col">
      First, but unordered
    </div>
    <div class="col order-12">
      Second, but last
    </div>
    <div class="col order-1">
      Third, but first
    </div>
  </div>
</div>

Example 2: change order columns bootstrap

<div class="row">
    <div class="col-md-3">
        sidebar
    </div>
    <div class="col-md-9 ">
        main
    </div>
</div>

//  CSS

.row{
   display: flex;
    flex-flow: column-reverse;
     }