Adjust code background colour to improve clarity in dark mode (#1828)

Author: UzairJ99

css/variables.css

@@ -45,7 +45,7 @@
   --notice-accent: #f9e8c3;
   --warn-bg: #4e2232;
   --warn-accent: #f9c3d6;
-  --code-bg: #181818;
+  --code-bg: #2b2b2b;
     /* support page related */
   --supported-fg:#299009;
   --eol-fg: #ff1a1a;