Recursive HTML Divs : I'm trying to figure out how to create recursive units strictly out of divs.

The root template would be (1). The (2) diagram is the expansion of the red rectangle in (1), and it is also the recursive template. 


How would it be possible to accomplish this using html/css and no bootstrap? Thanks. 


[![enter image description here][1]][1]


  [1]: https://i.stack.imgur.com/3eqSN.png