Hi,
Stylesheet for help files should be, they are real strangers within Moodle .
Ralf Hilgenstock asked for a solution some time ago. I added a JavaScript switch to the German helpfiles. If they are opened within Moodle the doc uses the selected theme CSS, if opened directly in a browser, the doc uses "docstyles.css". Perhaps you look at the files in "lang/de/docs/..." and see if you can start with that.