```js
// my-component.stories.js

import { html } from 'lit-html';

import './my-component';

import { INITIAL_VIEWPORTS } from '@storybook/addon-viewport';

export default {
  title: 'Stories',
  parameters: {
    //👇 The viewports object from the Essentials addon
    viewport: {
      //👇 The viewports you want to use
      viewports: INITIAL_VIEWPORTS,
      //👇 Your own default viewport
      defaultViewport: 'iphone6'
    },
  };
};

export const MyStory = () => html`<my-component></my-component>`;
MyStory.parameters = {
  viewport: {
    defaultViewport: 'iphonex'
  },
};
```