JSFiddle - React, Tailwind, and code Playground

HTML

<div class="parent">
    <div class="footer"></div>
</div>

CSS

.parent{
    width: 300px;
    height: 100%;
    background-color: grey;    
    margin: 0 auto;
}
html,body{
    height: 100%;
    padding: 0px;
    margin: 0px;
}
.footer{
    padding: 0px 15px;
    height: 50px;
    background-color: #1A1A1A;
    position:absolute;
    bottom: 0px;
    left: 0px;
    right: 0px;
}