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..