You can get basically the same thing from rebass in JS:

  <Box
    p={5}
    fontSize={4}
    width={[ 1, 1, 1/2 ]}
    color='white'
    bg='magenta'
  >
    Box
  </Box>

It uses a CSS-in-JS library under the hood to translate that into a CSS class for each unique combination of styling props.