Function track_style_over 

pub fn track_style_over(base: TrackStyle, attrs: &Attributes) -> TrackStyle

Read a <toggle> / <switch> track palette out of the cascaded attributes: the resting bg while unchecked, :checked { bg } while checked, :disabled { bg } while disabled.

base supplies each slot the cascade did not set: the built-in tokens at spawn, so a control is readable with no CSS at all, and the live palette on a restyle, so a theme flip that touches only one state leaves the others where markup put them.