Markdown to ePub - How to tweak styles?

Hi

Just joined the forum - have had pretty good success so far using ebook-convert to convert a markdown file to a mobi file - quite painless so far - impressed with the table of contents plugin feature.

Now I'm looking to do a few tweaks, and not quite sure how to approach this - or if this is the right forum. Apologies, if so.

In the manual here , I can see reference to the mobi-file-type option - but it doesn't give the exact values to use - and I can't work it out from the source code unfortunately. No idea how this works. Does anyone have a list of values for this, or an idea of how I'd work them out?

I also want to be able to make changes to the styling of the output.
Is there a way to see what stylesheet is being applied (I assume this is getting converted to html somewhere along the way) and is there a way I can override parts of the stylesheet - e.g. the H1 and H2s seem a bit big for my purposes, and I'd quite like to make the H2 a bit prettier.

I'd quite like to dig into how ebook-convert works (i.e. trace through the source code) as well, but no idea where to start in the source code! Any pointers appreciated.

Really happy to join the mobileread community - and really enjoying my time with Calibre so far - can't wait to dig deeper

Thanks

Simon.