JSFiddle - React, Tailwind, and code Playground

HTML

<div class='container'>
<input type='text' />
<div class='background'></div>
</div>

CSS

.container {
  border: red solid 1px; 
  position: relative;    
}
.background {
  position: absolute;
  background: grey;
  width: 100%;
  height: 100%;
  z-index: -1;
  top: 0;
  left: 0;   
}
input {
  margin: 10px;   
}
input:focus + .background {
  background: green;   
}