Not all systems have touchpads. Show keyboard instructions for triggering the overview and switching workspaces if no touchpad is present.
For now we assume that all touchpads support three-finger swipes.
This has a number of extremely big caveats:
gnome-settings-daemon (a boring C pkg-config library) and call two C functions, passing the result of one plus a constant to the other, and comparing the result to NULL. There is a comment indicating the equivalent C code which is needed. Perhaps a seasoned Rust expert would be able to fill this in relatively easily In the meantime (and for future testing),
TOUR_FORCE_TOUCHPAD=1 will cause the touchpad path to always be taken, and
TOUR_FORCE_TOUCHPAD=0 will cause the non-touchpad path to be taken. Hopefully this unblocks the strings & artwork.
.no-touchpad which can be used to distinguish in the CSS.