fix(list-group): background color is now transparent
fix(list-group): background color is now transparent

- background color is no longer white
- add class .bg-neutral-11 if a white background is desired
- $list-group-bg is now transparent

[Finishes #82482472]

npm/pivotal-ui,npm/pivotal-ui,sjolicoeur/pivotal-ui,CanopyCloud/pivotal-ui,pivotal-cf/pivotal-ui,sjolicoeur/pivotal-ui,npm/pivotal-ui,sjolicoeur/pivotal-ui,pivotal-cf/pivotal-ui,CanopyCloud/pivotal-ui,pivotal-cf/pivotal-ui,sjolicoeur/pivotal-ui,CanopyCloud/pivotal-ui