Image centering using flexbox technique

HTML

<div>
  <img src="https://placeholdit.imgix.net/~text?txtsize=33&txt=200%C3%97150&w=200&h=150"/>
</div>

CSS

div {
  width:800px;
  height:800px;
  border:2px solid #aaa;
  
  display:flex;
  justify-content:center;
  align-items:center;
}