JSFiddle - React, Tailwind, and code Playground

HTML

<div style="width:100%; height: 200px; background-color: grey;">
    <div class="inside">A</div>
    <div class="inside">B</div>
    <div class="inside">C</div>
    <div class="inside">D</div>
</div>

CSS

div.inside {
    width: 25%;
    float:left;
    border-right: 5px solid grey;
    background-color: blue;
    
    box-sizing:border-box;
    -moz-box-sizing:border-box; /* Firefox */
    -webkit-box-sizing:border-box; /* Safari */
}