I'm using compass, try to import my custom scss file in application.scss and have this error:

here my application.scss code:
/*
* This is a manifest file that'll be compiled into application.css, which will include all the files
* listed below.
*
* Any CSS and SCSS file within this directory, lib/assets/stylesheets, vendor/assets/stylesheets,
* or vendor/assets/stylesheets of plugins, if any, can be referenced here using a relative path.
*
* You're free to add application-wide styles to this file and they'll appear at the top of the
* compiled file, but it's generally better to create a new file per style scope.
*
*= require_self
*= require_tree
*/
@import "foundation_and_overrides";
@import "pnp";
if I remove require_tree error message will disappear but my scss file (pnp.scss) will not be loaded to the page
buttonmixin located? It seems yourpnpfile is trying to use it, but it cannot find it.