I can create buttons that allow a user to change the font, font size, and font color/background color for a page through JS. However, he would have to make those changes all over again for the next page.

What coding is involved to allow a user to change a CSS setting that applies to all pages during that session? I am talking about an offline app, so we can't use PHP/MySQL and similar technologies. HTML/CSS/JS is the best for this project, though localStorage can be used too.