<div id="block"></div>

#block {
  width: 20px;
  height: 20px;
  margin: 0 auto;
  background-color: blue;
  box-shadow: 4px 5px gray;
  /* You can also set the blur & spread values to 0 */
/*   box-shadow: 4px 5px 0 0 gray; */
}

/**
 Part of the "Creating Pixel Art with CSS" series by Jacque Schrag.
 Read the post: https://dev.to/jnschrag/creating-pixel-art-with-css-3451
**/