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

*{margin:0}
.center {
  display:table;
  width:100%;
  table-layout:fixed;
}
.center>*{
 display:table-cell;
 vertical-align:middle;
  border:solid;
}
h3 {
  font-size:60px;
}