Flex

<Flex
  mx={-3}
  flexWrap='wrap'>
  <Box width={[ 1, 1/2 ]} p={3} color='white' bg='blue'>
    Flex
  </Box>
  <Box width={[ 1, 1/2 ]} p={3} color='white' bg='violet'>
    Box
  </Box>
</Flex>