✨(react) add themes switching in Storybook

We want to be able to visualize easily themes directly inside
Storybook. This was not a trivial task as there is no centralized
logic to handle Doc / Stories / Manager at the same time.

packages/react/.storybook/themes.ts

@@ -0,0 +1,61 @@
+import { create } from '@storybook/theming';
+import { tokens } from '../src/cunningham-tokens';
+
+const buildTheme = (colors: typeof tokens.themes.default.theme.colors & any) => {
+    return {
+        brandUrl: 'https://github.com/openfun/cunningham',
+        brandImage: 'logo-cunningham.svg',
+        brandTitle: 'Cunningham',
+        brandTarget: '_self',
+
+        //
+        colorPrimary: colors['primary-400'],
+        colorSecondary: colors['primary-400'],
+
+        // UI
+        appBg: colors['greyscale-100'],
+        appContentBg: colors['greyscale-000'],
+        appBorderColor: colors['greyscale-300'],
+        appBorderRadius: 4,
+
+        // Text colors
+        textColor: colors['greyscale-900'],
+        textInverseColor: colors['greyscale-000'],
+
+        // Toolbar default and active colors
+        barTextColor: colors['greyscale-500'],
+        barSelectedColor: colors['greyscale-900'],
+        barBg: colors['greyscale-000'],
+
+        // Form colors
+        inputBg: colors['greyscale-000'],
+        inputBorder: colors['greyscale-300'],
+        inputTextColor: colors['greyscale-800'],
+        inputBorderRadius: 2,
+    };
+};
+
+export const themes = {
+    default: create({
+        base: 'light',
+        ...buildTheme(tokens.themes.default.theme.colors),
+    }),
+    dark: create({
+        base: 'dark',
+        ...buildTheme(tokens.themes.dark.theme.colors),
+    }),
+};
+
+export enum Themes {
+    dark = 'dark',
+    default = 'default'
+}
+
+export const BACKGROUND_COLOR_TO_THEME = {
+    '#0C1A2B': Themes.dark,
+};
+
+export const getThemeFromGlobals = (globals: any): string => {
+    const color = BACKGROUND_COLOR_TO_THEME[globals.backgrounds?.value];
+    return color ?? Themes.default;
+};