Stacked to horizontal with Bootstrap Grid System

Using a single set of .col-sm-* classes, you can create a basic grid system that starts out stacked and becomes horizontal at the small breakpoint (sm).

<div class="container">
  <div class="row">
    <div class="col-sm-8">col-sm-8</div>
    <div class="col-sm-4">col-sm-4</div>
  </div>
  <div class="row">
    <div class="col-sm">col-sm</div>
    <div class="col-sm">col-sm</div>
    <div class="col-sm">col-sm</div>
  </div>
</div>

References
https://getbootstrap.com/docs/4.3/layout/grid/#stacked-to-horizontal

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