JSFiddle - React, Tailwind, and code Playground

HTML

<button class="btn">Зачем тут JS?</button>

CSS

.btn {
  background: gray;
  width: 200px;
  height: 60px;
  display: block;
  border: 0;
  outline: 0;
  margin: 30px;
  cursor: pointer;
}

.btn:focus {
  background: black;
  color: white;
}