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// Contents in section conteiner in article container center horizontaly and vertically
article {
  display: inline-grid;
  grid-template-rows: 100px 100px 100px;
  grid-template-columns: 100px 100px 100px;
  grid-gap: 3px;
}

section {
  display: flex;
  justify-content: center;
  align-items: center;
  border: 2px solid black;
  font-size: 3em;
}


// Defalt - Contents in section container in article container align top left
article {
  display: inline-grid;
  grid-template-rows: 100px 100px 100px;
  grid-template-columns: 100px 100px 100px;
  grid-gap: 3px;
}

// Center section container horiaontaly (doesn't center the content directory) 
article {
  display: inline-grid;
  grid-template-rows: 100px 100px 100px;
  grid-template-columns: 100px 100px 100px;
  grid-gap: 3px;
  justify-items: center;
}

// Center section container horiaontaly and vertically (doesn't center the content directory) 
article {
  display: inline-grid;
  grid-template-rows: 100px 100px 100px;
  grid-template-columns: 100px 100px 100px;
  grid-gap: 3px;
  justify-items: center;
  align-items: center;
}

<article>
  <section>
    <div>X</div>
    <div>O</div>
    <div>X</div>
    <div>O</div>
    <div>X</div>
    <div>O</div>
    <div>X</div>
    <div>O</div>
    <div>X</div>
  </section>
</article>