Colorful indicator for each
_NavBarItem that animates back and forth
across the screen as the user taps.
Container for the most primitive data necessary to drive our animation with
functions to yield the next tier of calculated data for the animation.
Container for the state of a RollingNavBar's animation, useful for syncing
visual effects elsewhere in your app with nav bar animation progress.
Bottom nav bar with playful and customizable transitions between active