Function scroller_chrome 

pub fn scroller_chrome<R>(
    ui: &Ui,
    out: &ScrollAreaOutput<R>,
    outer: Rect,
    line: f32,
)

Repaint a shown vertical scroller NeXT-style: a knob with a 1 px bevel (white top-left, black bottom-right) above two grouped arrow buttons, each click scrolling line points. outer is the area plus its bar as laid out (out.inner_rect is the pre-shrink rect, so it can’t be used). The knob drags 1:1 with the pointer (ours, not egui’s whole-trough mapping), so it also works when the bar is drawn at a viewport edge egui’s own bar is scrolled away from (a grid wider than its window).