Check formatting of text in Redactor
There is a Redactor setting that should do what you’re looking for: 


  Stucture
  This settings introduces visual indicators for HTML tags h1-h6 and div, helping users understand the structure of the document.


https://imperavi.com/redactor/docs/settings/special/#setting-structure

Example editor:
https://imperavi.com/redactor/examples/structure/