JSFiddle - React, Tailwind, and code Playground

HTML

<div class="parent">
    <div class="child">Align to the bottom</div>
</div>

CSS

.parent {
    height: 300px;
    border: 5px solid #000;
    display: flex;
    flex-direction: column;
}
.child {
    height: 40px;
    width: 100%;
    background: #f00;
    margin-top: auto;
}