JSFiddle - React, Tailwind, and code Playground

HTML

<main>

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

</main>

CSS

* {
  box-sizing: border-box
}

html,
body {
  height: 100%;
  padding: 0;
  margin: 0;
}

main {
  display: flex;
  flex-wrap: wrap;
  margin: 20px;
  border-left: 1px solid violet;
  border-top: 1px solid violet;
}

div {
  width: 20%;
  height: 30px;
  border-right: 1px solid violet;
  border-bottom: 1px solid violet;
}