JSFiddle - React, Tailwind, and code Playground

HTML

<div class="col-sm-3 slots" style="background-color: red;">
    <div class="slot"></div>
    <div class="slot"></div>
    <div class="slot"></div>
    <div class="slot"></div>
</div>

CSS

.slots {
    width: 150px;
}
.slot {
    background:#00F;
    border: 1px solid #000;
    width: 100%;
    padding-bottom: 100%;
}