<article class="parent">
  <section>Centré</section>
</article>

<article class="parent">
  <section>Centré</section>
  <section>Centré</section>
  <section>Centré</section>
</article>

<article class="parent">
  <section style="width: 200px;">Centré</section>
  <section>Centré</section>
</article>

.parent {
  display: flex;
  justify-content: center;
}

article {
  border: 1px solid red;
  margin-bottom: 20px;
  padding: 10px 0px;
}

section {
  border: 1px solid blue;
}