Merge pull request #1143 from primer/storybook-overlay-fix

Minor storybook fixes for Overlay

src/stories/Overlay.stories.tsx

@@ -3,13 +3,17 @@ import React, {useState, useRef} from 'react'
 import {Meta} from '@storybook/react'
 import styled from 'styled-components'
 
+import {registerPortalRoot} from '../Portal'
 import {BaseStyles, Overlay, Button, Text, ButtonDanger, ThemeProvider, Position, Flex} from '..'
 
 export default {
   title: 'Internal components/Overlay',
   component: Overlay,
   decorators: [
     Story => {
+      // Since portal roots are registered globally, we need this line so that each storybook
+      // story works in isolation.
+      registerPortalRoot(undefined)
       return (
         <ThemeProvider>
           <BaseStyles>