message: Adds flex to Box props
diff: @@ -15,6 +15,7 @@ import {
  borderRadius,
  bgColor,
  textAlign,
  + flex,
  } from 'styled-system';
  import { neutralMargins } from 'react/styles/mixins';
  @@ -28,6 +29,7 @@ export const mixin = css`
  ${minHeight}
  ${maxHeight}
  ${space}
  + ${flex}
  ${alignItems}
  ${justifyContent}
  ${flexDirection}
  