JSFiddle - React, Tailwind, and code Playground

HTML

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

CSS

body {
    padding: 0px;
    margin: 0px;
    width: 100%;
    height: 100%;
}
body .footer {
    display: block;
    position: absolute;
    bottom: 0px;
    left: 0px;
    right:0px;
    width:auto;
    padding: 10px;
    background-color:red;
}
.footer .elem{
  background-color:blue;
}