How to use the rebass.Banner.extend function in rebass

import React from 'react'
import {Flex, Banner, Heading, Subhead} from 'rebass'
import {textGradient} from '../../theme'

import Logo from '../Logo'
import SearchBox from './SearchBox'

const CustomBanner = Banner.extend`min-height: 100vh;`

const CustomSubhead = Subhead.extend`
  ${textGradient} text-align: center;
  font-weight: normal;
  max-width: 40rem;
`

export default () => (
  
    
      
      
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