Good point. That's just one book design theme. Note: To change the typography e.g. the font used is just a single line in CSS ;-) Maybe you like the Rust theme better -> http://bookdesigns.github.io/book-rust or the Epsilon theme - http://bookdesigns.github.io/book-epsilon

PS: And, of course ;-), the idea is to contribute your own designs! It's really just an HTML template with some CSS.