storybook/docs/_snippets/addon-backgrounds-options-in-preview.md

export default {
  parameters: {
    backgrounds: {
      options: {
        // 👇 Default options
        dark: { name: 'Dark', value: '#333' },
        light: { name: 'Light', value: '#F7F9F2' },
        // 👇 Add your own
        maroon: { name: 'Maroon', value: '#400' },
      },
    },
  },
  initialGlobals: {
    // 👇 Set the initial background color
    backgrounds: { value: 'light' },
  },
};

// Replace your-renderer with the renderer you are using (e.g., react, vue3, angular, etc.)
import { Preview } from '@storybook/your-renderer';

const preview: Preview = {
  parameters: {
    backgrounds: {
      options: {
        // 👇 Default options
        dark: { name: 'Dark', value: '#333' },
        light: { name: 'Light', value: '#F7F9F2' },
        // 👇 Add your own
        maroon: { name: 'Maroon', value: '#400' },
      },
    },
  },
  initialGlobals: {
    // 👇 Set the initial background color
    backgrounds: { value: 'light' },
  },
};

export default preview;