JSFiddle - React, Tailwind, and code Playground

HTML

<div class="circle">
</div>

<div class="circle">
</div>


<div class="circle">
</div>

<div class="circle">
</div>

<div class="circle">
</div>

CSS

.circle {
  width: 100px;
  height: 100px;
  border: solid 3px black;
  border-radius: 100%;
  float: left;
  margin: 1%;
}

.effect {
  background-color: green;
  border-color: blue;
}

JavaScript

var circle = document.querySelectorAll(".circle");

for (var i = 0; i < circle.length; i++) {
  (function(x) {
    circle[x].addEventListener('click', function() {
      this.classList.toggle('effect')
    })

  }(i))
}