Button.js

import React, {PureComponent} from 'react';
import PropTypes from 'prop-types';
import styled, {css} from 'styled-components';

export default class Button extends PureComponent {
  render () {
    return <ButtonStyped>{this.props.title}</ButtonStyped>;
  }
}

const ButtonStyped = styled.button`
${props => props.rounded && css`
border-radius: 5px
`}
background-color: ${props => (props.primary ? '#264e86' : '#eff0f4')};
color: ${props => (props.primary ? 'white' : '#264e86')};
padding: 10px;
margin: 3px;
font-size: 1em;
outline: none
`;

Button.defaultProps = {
  title: 'Hello!',
  primary: true,
  rounded: false,
};

Button.propTypes = {
  title: PropTypes.string.isRequired,
  primary: PropTypes.bool,
  rounded: PropTypes.bool,
};