Refactor: Update CSS Custom Properties prefix to --givewp

[kjohnson]

Description

This PR updates all GiveWP CSS custom properties to use the --givewp prefix for consistency with the CSS class name prefix.

Visuals

-    --give-primary-200: #E6FFE6;
-    --give-primary-300: #C2F2C3;
-    --give-primary-400: #AAF2AC;
-    --give-primary-500: #68BF6B;
-    --give-primary-600: #15AE56;
-    --give-primary-700: #5BA65E;
-    --give-primary-800: #3F7341;
+   --givewp-primary-200: #E6FFE6;
+   --givewp-primary-300: #C2F2C3;
+   --givewp-primary-400: #AAF2AC;
+   --givewp-primary-500: #68BF6B;
+   --givewp-primary-600: #15AE56;
+   --givewp-primary-700: #5BA65E;
+   --givewp-primary-800: #3F7341;

[jonwaldstein]

💯