OZG-6908 Use backdrop color in tailwind config

alfa-client/libs/design-system/src/lib/tailwind-preset/tailwind.config.js

@@ -127,7 +127,7 @@ module.exports = {
         mainbg: 'hsl(var(--color-mainbg) / <alpha-value>)',
         modalBg: 'hsl(var(--color-modal-bg) / <alpha-value>)',
         dropdownBg: 'hsl(var(--color-dropdown-bg) / <alpha-value>)',
-        grayBackdrop: 'hsla(var(--color-gray-dropdown))',
+        grayBackdrop: 'hsla(var(--color-gray-backdrop))',
         primary: {
           600: 'hsl(var(--color-primary-600) / <alpha-value>)',
           DEFAULT: 'hsl(var(--color-primary-600) / <alpha-value>)',