JSFiddle - React, Tailwind, and code Playground

HTML

<div>
  <p>dupa</p>
  <div id="footer">
     <p>text</p>
  </div>
</div>

CSS

html, body {
    height: 100%;
    width: 100%;
    margin: 0;
    padding: 0;
}

body {
  position: relative;
}

div {
    background-color: red;
    width: 100%;
    height: 100%;
    border: 1px solid black;
    box-sizing: border-box;
    -webkit-box-sizing: border-box;
    -moz-box-sizing: border-box;
}

#footer {
  background-color: black;
  color:white;
  height: 30px;
  display: flex;
  align-items: center;
  position: relative;
  bottom: 0;
}