How to center align a div horizontally and vertically both.

Let's say you have a code

<div id='parent'>
   <div id='child'>hello</div>
</div>

and you want to make the child element to be centered horizontally and vertically both. How will you do that??
Actually it's pretty simple.

#parent {
    display: grid;
    place-items: center;
}

and it's done. Bbye..