DEV: Use CSS custom properties for colors in SCSS

DEV: Use CSS custom properties for colors in SCSS

Prepares the plugin for an upcoming change in core while maintaining backwards compatiblity.

diff --git a/assets/stylesheets/cakeday.scss b/assets/stylesheets/cakeday.scss
index c87b350..8196307 100644
--- a/assets/stylesheets/cakeday.scss
+++ b/assets/stylesheets/cakeday.scss
@@ -30,7 +30,7 @@
     }
 
     .user-info-empty-message {
-      color: $primary-high;
+      color: var(--primary-high, $primary-high);
       padding-bottom: 30px;
     }
   }

GitHub sha: c36bb9ad