JSFiddle - React, Tailwind, and code Playground

HTML

<div class="gridcontainer">
    <div class="griditem"></div><div class="griditem"></div><div class="griditem"></div><div class="griditem"></div><div class="griditem"></div><div class="griditem"></div><div class="griditem"></div><div class="griditem"></div><div class="griditem"></div><div class="griditem"></div><div class="griditem"></div><div class="griditem"></div><div class="griditem"></div><div class="griditem"></div><div class="griditem"></div><div class="griditem"></div>
</div>

CSS

div.gridcontainer {
    width: 80px;
    line-height: 0;
}

div.griditem {
    display: inline-block;            
    border-bottom: 1px solid black;
    border-right: 1px solid black;
    width: 18px;
    height: 18px;
}

div.griditem:nth-child(4n+1) {
    border-left: 1px solid black;
}

div.griditem:nth-child(-n + 4) {
    border-top: 1px solid black;
}