I’d advise a book a Scrivener Themes, because that’s the way to modify the UI. If you want readymade Themes, go to the Windows Themes post.
For terminology, the Scrivener Manual in the Help menu is the place to go, The general workings of Scrivener is best explained in the Interactive Tutorial, also from the Help menu.
With Themes you won’t get HTML, but you will be able to change a QSS stylesheet, similar to CSS Stylesheets.