how to ensure the element center in css code example

Example: css center div

<!-- 
	 Simple CSS CENTER DIV Example
 	 
	 * See Fiddle in link for PoC *
-->

<div class="parent">
  <div class="child">
    <p>
      Eh Up Me Duck!
    </p>
  </div>
</div>

<style>
.parent {
  /* Just for aesthetics: see fiddle */
  border: 1px solid black;
  padding: 2px;
}

.child {
  border: 1px solid red;
  width: 50%;
  
  /* This is where the magic happens */
  margin-left: auto;
  margin-right: auto;
  /**********************************/
}

p {
  /* As you do */
  text-align: center;
}
</style>