chore: Update storybook settings to widget stories (#7595)

.storybook/main.js

@@ -23,6 +23,18 @@ module.exports = {
     },
     '@storybook/addon-links',
     '@storybook/addon-essentials',
+    {
+      /**
+       * Fix Storybook issue with PostCSS@8
+       * @see https://github.com/storybookjs/storybook/issues/12668#issuecomment-773958085
+       */
+      name: '@storybook/addon-postcss',
+      options: {
+        postcssLoaderOptions: {
+          implementation: require('postcss'),
+        },
+      },
+    },
   ],
   webpackFinal: config => {
     const newConfig = {
@@ -35,7 +47,7 @@ module.exports = {
 
     newConfig.module.rules.push({
       test: /\.scss$/,
-      use: ['style-loader', 'css-loader', 'sass-loader'],
+      use: ['style-loader', 'css-loader', 'postcss-loader', 'sass-loader'],
       include: path.resolve(__dirname, '../app/javascript'),
     });