JSFiddle - React, Tailwind, and code Playground

HTML

<div class="flex">
    <div class="header">Sweet header</div>
    <div class="content">Main content
        <div class="bottom">
          This guy should be fixed above the footer.
        </div>
    </div>
    
    <div class="footer">Equally sweet footer</div>
</div>

CSS

.flex{
	border: 1px solid #ddd;
	font: 14px Arial;
	display: flex;
	flex-direction: column;
}

.header{
  background : #007AA2;
  flex: 0 0 auto;
}

.content{
  background : #FFF;
  flex: 1 1 auto;
  height: 200px;
}

.footer{
  background : #7FCADE;
  flex: 0 0 auto;
}

.bottom {
  position: absolute;
  bottom: 20px;
}