If you need to manually add an addon in Storybook, you can follow these steps to get going. First, we’ll need to install the addon in question.

 npm i -D @storybook/addon-themes

Next, we’ll pop over to .storybook/main.ts and add it to the array of addons.

diff --git a/.storybook/main.ts b/.storybook/main.ts
index 098b7b7..63965e0 100644
--- a/.storybook/main.ts
+++ b/.storybook/main.ts
@@ -8,6 +8,7 @@ const config: StorybookConfig = {
     '@storybook/addon-essentials',
     '@chromatic-com/storybook',
     '@storybook/addon-interactions',
+    '@storybook/addon-themes',
   ],
   framework: {
     name: '@storybook/react-vite',