JSFiddle - React, Tailwind, and code Playground

HTML

<div id = "btn" onclick ="toShadow">click to change shadow; click again to change back</div>

CSS

#btn {
  height: 20px;
  border: 2px solid black;
  box-shadow: 5px 5px black; 
}

JavaScript

var btn = document.getElementById("btn");

function toShadow(){
document.getElementById("btn").style.boxShadow="5px 5px red"
}