JSFiddle - React, Tailwind, and code Playground

HTML

<div id="partie1" class="partie">
  <div class="center">
    <p class="para">
      Mon paragraphe
      </p>
    <h3>Titre H1 : Mon titre</h3>
  </div>
</div>
<div id="partie2" class="partie">
  <div class="center">
    <p class="para">
      Mon paragraphe
    </p>
    <h3>Mon titre</h3>
  </div>
</div>

CSS

.center {
  display:flex;
  align-items:center;
}
.center>*{
  flex:1;
  border:solid;
}
h3 {
  font-size:60px;
}