message: Allow color and flex props to be set on Dialog.Header
diff: @@ -7,7 +7,7 @@ import {space, color} from 'styled-system'
  import systemPropTypes from '@styled-system/prop-types'
  import {X} from '@primer/octicons-react'
  import StyledOcticon from './StyledOcticon'
  -import {get, LAYOUT} from './constants'
  +import {LAYOUT} from './constants'
  import theme from './theme'
  import Text from './Text'
  import Flex from './Flex'
  @@ -54,7 +54,6 @@ const UnstyledButton = styled(Flex).attrs({
  const DialogHeader = styled(Flex).attrs({
  p: 3,
  - bg: 'gray.1',
  justifyContent: 'space-between',
  alignItems: 'center'
  })`
  @@ -102,16 +101,21 @@ Dialog.propTypes = {
  theme: PropTypes.object
  }
  -DialogHeader.defaultProps = {theme}
  +DialogHeader.defaultProps = {
  + alignItems: 'center',
  + bg: 'gray.1',
  + justifyContent: 'space-between',
  + theme
  +}
  DialogHeader.propTypes = {
  - theme: PropTypes.object
  + ...Flex.propTypes
  }
  DialogHeaderText.defaultProps = {theme}
  DialogHeaderText.propTypes = {
  - theme: PropTypes.object
  + ...DialogHeader.propTypes
  }
  Dialog.Header = DialogHeader
  