message: make top nav sticky, simplify App
diff: import React from 'react'
  -import {ThemeProvider} from 'emotion-theming'
  import PropTypes from 'prop-types'
  import {NavLink} from 'react-router-dom'
  import Styles from './doc-components/Styles'
  import Octicon, {Package} from '@githubprimer/octicons-react'
  -import {Box, Link, Text, UnderlineNav, UnderlineNavLink, theme} from '../src'
  +import {Box, Link, Sticky, Text, UnderlineNav, UnderlineNavLink} from '../src'
  import {name, repository, version} from '../package.json'
  const pkg = `${name}@${version}`
  @@ -13,9 +12,7 @@ const releaseURL = `https://github.com/${repository}/releases/v${version}`
  export default function Page({render}) {
  return (
  <React.Fragment>
  - <Styles />
  - <ThemeProvider theme={theme}>
  - <Box color="bodytext">
  + <Sticky bg="white">
  <UnderlineNav
  actions={
  <Text color="gray.5" fontFamily="mono" px={4}>
  @@ -34,9 +31,9 @@ export default function Page({render}) {
  Sandbox
  </UnderlineNavLink>
  </UnderlineNav>
  + </Sticky>
  <Box p={3}>{render()}</Box>
  - </Box>
  - </ThemeProvider>
  + <Styles />
  </React.Fragment>
  )
  }
  