You can keep the “template.css.tmpl” file name with…
{{ with resources.Get "template.css.tmpl" }}
{{ with .Content | resources.FromString "css/main.css" }}
{{ with . | resources.ExecuteAsTemplate "css/main.css" $ }}
{{ with . | resources.Minify }}
<link rel="stylesheet" href="{{ .RelPermalink }}">
{{ end }}
{{ end }}
{{ end }}
{{ end }}
Though if it were my project I’d keep the “template.css” file name and be done with it.