HTML or/and CSS codes to construct numbered paragraphs.

I'm trying to construct a HTML document with a layout similar to the example above.  Indented hanging paragraph with following sub-indented hanging paragraphs below.  Not quite sure if the term hanging indent applies here.  The outer paragraphs are numbered and the inner ones as well but with letters.  Note that the numbering does not have to be done automatically, I can type those.

I can do this with tables (lots of colspans and rowspans involved) but it gets very messy.

But there might be a (simple) way in HTML or CSS to do this that my Google searches can't find.