Function step 

pub fn step(theme: &Theme, icon: impl Into<Icon>, enabled: bool) -> Div

Previous or next, with icons::glyph::ChevronLeft/icons::glyph::ChevronRight — the pair the calendar’s month header already uses.

A disabled step stays in place rather than disappearing at the ends, so the row does not shuffle sideways on the first and last pages. Paints only: the caller wires the click, and ignores it when not enabled.