For custom.css file in Astroid 2.6.1 you can use following path
- images/{template}/css
- templates/{template}/css
- media/templates/site/{template}/css
My problem is not the custom.css file but the styles list in a lot of sites with Astroid One, Zero and some of your templates: with JCE that list is empty.
The custom.css in both template or media/templates/sites is well used to personalize the site.
This morning I checked 16 remote sites and I explain the results on the Github discussion.