storybook/docs/snippets/web-components/component-story-custom-params.js.mdx

```js
// Button.stories.js

export default {
  title: 'Button',
  component: 'demo-button',
};

export const Primary = {
  args: {
    primary: true,
    label: 'Button',
  },
  parameters: {
    backgrounds: {
      values: [
        { name: 'red', value: '#f00' },
        { name: 'green', value: '#0f0' },
        { name: 'blue', value: '#00f' },
      ],
    },
  },
};
```