how to align everything in center html code example

Example 1: css align center

//HTML
<div class="parent">
	<span>Hello World</span>
</div>

//CSS
.parent {
  display: flex;
  justify-content: center;
  align-items: center;
}

Example 2: html center text

<div style="text-align:center">Dieser Text wird zentriert.
<p>Ebenso dieser Paragraph.</p></div>