add dark mode

.storybook/preview.ts

@@ -2,11 +2,24 @@ import '@fontsource/roboto/400.css'
 import '@fontsource/roboto/700.css'
 import '../src/styles/index.scss'
 
+import { themes } from '@storybook/theming'
 import type { Preview } from '@storybook/react'
 
 const preview: Preview = {
   parameters: {
     actions: { argTypesRegex: '^on[A-Z].*' },
+    docs: {
+      theme: themes.dark,
+    },
+    backgrounds: {
+      default: 'dark',
+      values: [
+        {
+          name: 'dark',
+          value: '#000000',
+        },
+      ],
+    },
     controls: {
       matchers: {
         color: /(background|color)$/i,