Change navigation highlight to neutral light grey without gradient

Co-authored-by: ralfhandl <[email protected]>

Author: Copilot

_sass/custom/custom.scss

@@ -30,7 +30,7 @@
     --search-bg: #302d36;
     --base-button: #302d36;
     --nav-text: #e6e1e8;
-    --nav-highlight: #44434d;
+    --nav-highlight: #3d3d3d;
     --aux-nav-bg: #27262b;
   }
 }