Looks interesting. A little bit of feedback: - I didn't like that the table of contents disappeared on me when I clicked on a page. - Related to this, it would be great for the progress widget to show the actual name of each page/chapter, if not all the time, at least when you hover with the mouse. - In the table on contents: mark in some way the links that are going to take you away from the book and into a github view. - The Next button feels too big in pc. Takes away the attention from the content itself. Thank you for your hard work!