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/patreon.scss b/assets/stylesheets/patreon.scss
index c16dd38..d14a163 100644
--- a/assets/stylesheets/patreon.scss
+++ b/assets/stylesheets/patreon.scss
@@ -32,7 +32,7 @@
   clear: both;
   padding: 15px;
   border-radius: 3px;
-  background-color: $tertiary-low;
+  background-color: var(--tertiary-low, $tertiary-low);
   box-sizing: border-box;
   margin: 15px 0;
 

GitHub sha: ee88db40