JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
  <div class="a">A</div>
  <div class="b">B</div>
</div>

CSS

.container {
  display: flex;
  flex-direction: column;
}
.a {
  margin: 0 auto;
  border: 1px solid red;
}
.b {
  border: 1px solid blue;
}