precompile css warning info

Created by: itxx00

gitlab version: 5-4-stable

when run 'bundle exec rake assets:precompile RAILS_ENV=production' I can get warning info in log file. in log/production.log:

WARNING on line 42 of /home/git/gitlab/app/assets/stylesheets/sections/merge_requests.scss: ".automerge_widget .how_to_merge_link" failed to @extend ".primary".
  The selector ".primary" was not found.
  This will be an error in future releases of Sass.
  Use "@extend .primary !optional" if the extend should be able to fail.

WARNING on line 53 of /home/git/gitlab/app/assets/stylesheets/sections/notes.scss: "ul.notes .discussion .discussion-body .file" failed to @extend ".borders".
  The selector ".borders" was not found.
  This will be an error in future releases of Sass.
  Use "@extend .borders !optional" if the extend should be able to fail.

WARNING on line 53 of /home/git/gitlab/app/assets/stylesheets/sections/notes.scss: "
 ul.notes .discussion .discussion-body .discussion-hidden" failed to @extend ".borders".
  The selector ".borders" was not found.
  This will be an error in future releases of Sass.
  Use "@extend .borders !optional" if the extend should be able to fail.

WARNING on line 53 of /home/git/gitlab/app/assets/stylesheets/sections/notes.scss: "
 ul.notes .discussion .discussion-body .notes" failed to @extend ".borders".
  The selector ".borders" was not found.
  This will be an error in future releases of Sass.
  Use "@extend .borders !optional" if the extend should be able to fail.

WARNING on line 30 of /home/git/gitlab/app/assets/stylesheets/sections/editor.scss: ".file-editor .commit-button-annotation .commit-btn" failed to @extend ".save-btn".
  The selector ".save-btn" was not found.
  This will be an error in future releases of Sass.
  Use "@extend .save-btn !optional" if the extend should be able to fail.