JSFiddle - React, Tailwind, and code Playground

HTML

<div class="parent">
  <div class="child">Hi!</div>
</div>

CSS

.parent {
  display: flex;
  height: 300px;
  width: 300px;
  background: green;
  justify-content: center;
  align-items: center;
}
.child {
  height: 50px;
  width: 50px;
  background: grey;
  margin: 0 0 0 0;
  margin-top: 0;
  margin-bottom: 0;
  margin-left: 0;
  margin-right: 0;
}