// set up navigation buttons and text for them
Restart
Next
// title at top of chart
2017 Fuel Economy Averages by Engine Type - Introduction
//initial state's explanation text
This narrative will guide you through an exploration
of the highway and city average fuel economies of
2017 model year cars by engine type
Navigate forward by clicking the "Next" button below
or "Restart" to go back to the beginning.
// Make Color Legend, start with opacity=0 in initial state
Color Key
Blue: Gasoline
Yellow: Diesel
Green: Electric