JSFiddle - React, Tailwind, and code Playground

by Michel Penke

HTML

<style>
.btn {-webkit-tap-highlight-color: transparent;
  background-color: #fff;
  border: 1px solid #ff5064;
  border-radius: 20px;
  box-shadow: none;
  box-sizing: border-box;
  color: #000;
  display: inline-block;
  font-size: 15px;
  font-weight: 700;
  line-height: 1;
  padding: 12px 24px;
  text-align: center;
  text-decoration: none;
  transition-delay: 0s;
  transition-duration: .5s;
  transition-property: all;
  transition-timing-function: ease;
  width: auto;}</style>
  
  
  <div class="btn" id="btn" onclick="testfunction()">Test </div>
  <div class="proof" id="box">Proof</div>

<script>function testfunction() {
  var btn = document.getElementById('btn');
  var box = document.getElementById('box');
  btn.onclick = function() {
    box.addClass("test");
  }
}
</script>

CSS

.test {color: red;}