text: Title: HTML/CSS - Fix right bar in docs
  Body: When opening in a large monitor, the docs display a right bar to move between sections ([example](https://ploomber.readthedocs.io/en/latest/user-guide/deployment.html)):
  
  
  ![Screen Shot 2021-10-15 at 12 24 27](https://user-images.githubusercontent.com/989250/137521183-9d530088-442f-438c-a21e-02748b199175.png)
  
  However, on tablets and phones, we remove that bar. It'd be better to add a button to the top bar to toggle it, just like we do with the left bar (see right button):
  
  ![Screen Shot 2021-10-15 at 12 25 33](https://user-images.githubusercontent.com/989250/137521225-e9be7f67-a5a8-4572-bd70-aec0790234ef.png)
  
  source code: https://github.com/ploomber/ploomber/blob/76b2abf78092e6696d9e25e47cefdc1e1589529f/doc/_templates/layout.html#L41
  
  check doc/contributing.md for instructions
  