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/code_review.scss b/assets/stylesheets/code_review.scss
index 7685c3a..db7de4f 100644
--- a/assets/stylesheets/code_review.scss
+++ b/assets/stylesheets/code_review.scss
@@ -12,7 +12,7 @@ tbody {
         align-items: baseline;
 
         .committer {
-          color: $primary-high;
+          color: var(--primary-high, $primary-high);
           font-size: $font-down-1;
           font-weight: bold;
           margin-right: 12px;
@@ -24,11 +24,11 @@ tbody {
         }
 
         .approved {
-          color: $success;
+          color: var(--success, $success);
         }
 
         .followup {
-          color: $danger;
+          color: var(--danger, $danger);
         }
 
         .pending {

GitHub sha: 182717a0