Button.js

import React from 'react';
import classNames from 'classnames';
import './Button.css';

function Button(props) {
  const {
    children,
    className, // <-- destructure the className passed in
    outline,
    primary
  } = props;

  const classes = classNames(
    'button',
    className, // <-- pass it to classNames()
    {
      'button--outline': outline && !primary,
      'button--outline-primary': outline && primary,
      'button--primary': !outline && primary,
    }
  );

  return (<button className={classes}>{children}</button>);
}
          
export default Button;