title: What's the document loader used on Youtube?
body: <p>I want to use a loader such as the one on Youtube before the content is loaded. On youtube, every piece of content uses a light gray color loader before rendering the actual content. It is made of squares and circles to simulate the actual content about to be rendered.</p>
  
  <p>Do you know what it is ? Surprisingly, I couldn't find it neither on material-ui nor via a google search.</p>