Love this. Small suggestion for mobile UX: either hide the system keyboard, or allow the user to hear the currently selected typewriter sounds for their system keyboard taps. Not sure this is intended behaviour, but typing on mobile gives a generic click unless I use the poky on-page keyboard and thus lose the muscle memory needed to type quickly or accurately.

Also navigating back in mobile browser should close the active keyboard as on a small screen it looks like you are on a new page so it's surprising when back throws you out of the site.