title: Masonry grid using flexbox
body: <p>I need a masonry grid like this: </p>
  
  <p><img src="https://i.stack.imgur.com/kkUsi.jpg" alt="masonry grid"></p>
  
  <p>Is this possibile to achieve that using flexbox only? Or any other way? 
  Don't want to use Masonry library or other library or framework. </p>