According to my test results, Sass css processing (and import partials) is working in custom themes, but not in custom portlet plugins.
This is the current load path:
I think there are 2 problems with the load path of the Sass processor in custom portlets:
1) Sass looks for partial in the css folder of the current layout's theme, but in a wrong base folder: "/temp/2-sample-portlet/html/themes/classic/css"
It should be fixed like this: "/webapps/ROOT/html/themes/classic/css"
2) Sass doesn't looking for partial in the css folder of the custom portlet
This path should be included in load path: "/temp/2-sample-portlet/css"