Use CSS custom properties for SCSS colors

Use CSS custom properties for SCSS colors

diff --git a/assets/stylesheets/user_notes.scss b/assets/stylesheets/user_notes.scss
index c3fdf8d..6d25dc1 100644
--- a/assets/stylesheets/user_notes.scss
+++ b/assets/stylesheets/user_notes.scss
@@ -41,7 +41,7 @@
   }
 
   .user-note {
-    border-top: 1px solid $primary-low;
+    border-top: 1px solid var(--primary-low, $primary-low);
     padding-top: 1em;
 
     &:first-of-type {

GitHub sha: 87971bbb