message: update button group
diff: import styled from 'styled-components'
  +import {get} from './constants'
  import Box from './Box'
  const ButtonGroup = styled(Box)`
  @@ -10,8 +11,8 @@ const ButtonGroup = styled(Box)`
  border-radius: 0;
  :first-child {
  - border-top-left-radius: 3px;
  - border-bottom-left-radius: 3px;
  + border-top-left-radius: ${get('radii.2')};
  + border-bottom-left-radius: ${get('radii.2')};
  margin-right: 0;
  }
  @@ -22,8 +23,8 @@ const ButtonGroup = styled(Box)`
  :last-child {
  border-right-width: 1px;
  - border-top-right-radius: 3px;
  - border-bottom-right-radius: 3px;
  + border-top-right-radius: ${get('radii.2')};
  + border-bottom-right-radius: ${get('radii.2')};
  }
  :focus,
  