With egui 0.13.0, it is impossible to set a custom Stroke for the HLine and VLine plot items, since there is no setter method on either of those. (Line does however have setter methods for the stroke, stroke width, and stroke color.)

I'm not sure if this was an oversight as part of the plot widget overhaul or an intended API change - if it was unintentional, I'd be happy to PR the missing setters!