content: import React from 'react';
  import IconButton from './IconButton';
  import { hashHistory } from 'react-router';
  
  const BackButton = ({ lightness }) => (
      <IconButton
          iconName={'back'}
          iconSize={24}
          iconClassName={`icon_${lightness}`}
          clickHandler={hashHistory.goBack}
      />
  );
  
  BackButton.propTypes = {
      lightness: React.PropTypes.string
  };
  
  export default BackButton;
  