Currently the CSS stylesheet is hard-coded to the one coming with the software, the one from https://kevinburke.bitbucket.io/markdowncss/. It would be nice to be able to override this with some custom stylesheet, e.g. defined via some config file.
I would like to see this implemented as well. Notepad++ markdown plugin has this, and it is really nice. The Notepad++ markdown plugin, can export the file to an (html) file as well.