JSFiddle - React, Tailwind, and code Playground

HTML

<div><b></b><b></b><b></b><b></b></div>

CSS

body {
  background: #f3f5f6;
}

div {
  font-size: 15px;
  width: 401px;
  margin: 20px;
  background: #fff;
  display: flex;
  flex-wrap: wrap;
}

b {
  height: 50px;
  background: red;
  width: calc((100% - 4.5em) / 4); /* .5em gutters */
  margin-bottom: 1.5em;
}

b:not(:last-child) {
  margin-right: 1.5em;
}