JSFiddle - React, Tailwind, and code Playground

HTML

<div class="main">
  <div class="box">1</div>
</div>

CSS

.main {
  background: #999;
  margin: 0 auto;
  width: 500px;
  display: flex;
  flex-wrap: wrap;
}
.box {
  background: #7ab9d7;
  color: #555;
  height: 30px;
  width: 30%;
  margin-bottom: 30px;
  text-align: center;
  font-size: 30px;
  padding-top: 120px;
}
.box:not(:nth-child(3n)) {
  margin-right: 5%;
}
.box:only-child {
  margin-right: auto;
  margin-left: auto;
}