ui: improve bg-active contrast

styles/vars.css

@@ -13,7 +13,7 @@
 
 .dark {
   --c-bg-base: #111;
-  --c-bg-active: #151515;
+  --c-bg-active: #191919;
   --c-bg-code: #ffffff06;
   --c-text-base: #fff;
   --c-text-secondary-light: #555;