Papermod Theme: How to add custom CSS?

Thanks I see

{{- $common := (resources.Match “css/.css") | resources.Concat “assets/css/common.css” }}
{{- $extended := (resources.Match "css/extended/
.css”) | resources.Concat “assets/css/extended.css” }}
{{- /* bundle all required css /}}
{{- /
Add extended css after theme style */ -}}
{{- $stylesheet := (slice $common $extended) | resources.Concat “assets/css/stylesheet.css” | minify }}

I guess the css bundling happens with theme css but not css added to the site?

The theme provides an extend_head.html file that is blank except for comments so I guess I will copy this file to my site and then add the css file there.