JSFiddle - React, Tailwind, and code Playground

HTML

<div class="parent">
  <button class="primary">Bouton centré avec test plutôt long pour s'en rendre compte</button>
  <button class="secondary">Bouton à coté</button>
</div>

CSS

body {
  display: flex;
  justify-content: center;
}

.parent {
  background-color: #eee;
  height: 300px;
  width: 50%;
  
  display: flex;
  justify-content: center;
  align-items: center;
}

.primary {
  background-color: #55dd77;
  border: none;
  height: 2rem;
}

.secondary {
  background: none;
  border: none;
  text-decoration: underline;
  margin-left: 2rem;
}