Scroll from sunrise to night through a fixed sky
Four full-height sections labelled Sunrise, Day, Sunset and Night sit over one fixed sky. Scroll drives the gradient, the clouds and the star field, and the labels flip from ink to paper near the end.
The gradients interpolate between four hand-picked stops rather than compute from a time of day, which is the only way to make the muddy pink of dusk look like dusk. Nothing runs on a timer, so scrolling up runs the day backwards.