JSFiddle - React, Tailwind, and code Playground

HTML

<button id="b1" class="bouton">Autre monde ...</button>

CSS

.bouton {

  background-color: #FFFF00;
  border-radius: 50px;
  border-width: 20;
  box-shadow:
    rgba(25, 25, 25, 0.04) 0 0 1px 0,
    rgba(0, 0, 0, 0.1) 0 3px 4px 0;
  color:
    #0099FF;
  cursor: pointer;
  display: inline-block;
  font-family: Arial, sans-serif;
  font-size: 15px;
  height: 30px;
  padding: 0 25px;
}

.variant {
  background-color: #0099FF;
  color: #FFFF00;
}

JavaScript

const b1 = document.getElementById("b1");
b1.addEventListener("click", changeColor);

function changeColor() {
  b1.classList.toggle('variant')
};