JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta/css/bootstrap.min.css">
<div class="d-flex flex-column container-fluid test-container">
  <div class="row align-items-start align-content-start">
    <div class="col-md-4">R1-C1</div>
    <div class="col-md-4">R1-C2</div>
    <div class="col-md-4">R1-C3</div>
  </div>

  <div class="row align-items-start align-content-start">
    <div class="col-md-4">R2-C1</div>
    <div class="col-md-4">R2-C2</div>
    <div class="col-md-4">R2-C3</div>
  </div>
</div>

CSS

.test-container {
  height: 100vh;
}
.test-container .row > div {
  border: 1px dashed lightgray;
}
.test-container .row:first-child,
.test-container::after {
  content: '';
  flex: 1 1 0;
}