Well, they do have options to override the CSS. That's what the font, line spacing and and margins settings do. And if you are reading kepubs, there is a user style file that will override them.
But, I think the real reason they don't have more than this is that it will break to many books. Or not do what is expected. To do it properly, you need to understand how the book was constructed. Otherwise, you make a change and loose information. Plus there are other ways to do this.
|