geom_point(color_off), stroke-width too small to see stroke change

[tdhock]

here is a simple example which uses alpha_off and color_off, with both points and tiles, https://bl.ocks.org/tdhock/raw/0c6fc15834620a391d281ef8be7587d5/
source: https://github.com/tdhock/animint-book/blob/master/Ch06-other.Rmd#L378
seems like everything is working as expected, using code from #72
but for the case of geom_point -> svg circle it is hard to see the color -> stroke change, so I am wondering if we can easily add a geom param which controls stroke-width style?