Storybook: fix theme colors not updating (#40679) (#40691)

(cherry picked from commit 1e471a6f76)

Co-authored-by: Jack Westbrook <jack.westbrook@gmail.com>

packages/grafana-ui/.storybook/preview.ts

@@ -39,8 +39,8 @@ export const parameters = {
     container: ThemedDocsContainer,
   },
   darkMode: {
-    dark: GrafanaDark,
-    light: GrafanaLight,
+    dark: { ...GrafanaDark, base: 'dark' },
+    light: { ...GrafanaLight, base: 'light' },
   },
   layout: 'fullscreen',
   actions: { argTypesRegex: '^on[A-Z].*' },

packages/grafana-ui/.storybook/storybookTheme.ts

@@ -5,8 +5,6 @@ import '../src/components/Icon/iconBundle';
 
 const createStorybookTheme = (theme: GrafanaTheme2) => {
   return create({
-    base: theme.name.includes('Light') ? 'light' : 'dark',
-
     colorPrimary: theme.colors.primary.main,
     colorSecondary: theme.colors.error.main,