You are looking to modify the EdgeForm
of your barsChartStyle
, and this is shown in the documentation for Histogram
, in the Options
section.
SeedRandom[42];
data = RandomVariate[NormalDistribution[0, 1], 200];
Histogram[data,
ChartStyle -> {EdgeForm[
Directive[AbsoluteThickness[2], Black, Opacity[1]]]}]