message: add m + p utils to Dropdown
diff: import React from 'react'
  import PropTypes from 'prop-types'
  +import classnames from 'classnames'
  import Details from './Details'
  import Button from './Button'
  import Caret from './Caret'
  +import {mapWhitespaceProps} from './props'
  const arrowStyles = {
  content: '',
  @@ -14,9 +16,10 @@ const arrowStyles = {
  height: '0'
  }
  -export default function Dropdown({title, scheme, children}) {
  +export default function Dropdown(props) {
  + const {title, scheme, children, className} = mapWhitespaceProps(props)
  return (
  - <div className="BtnGroup">
  + <div className={classnames(className, 'BtnGroup')}>
  <Details className="details-reset BtnGroup-form d-flex">
  {({toggle}) => (
  <React.Fragment>
  