app.js

<Dropdown>
  <DropdownItem to="/projects">My Projects</DropdownItem>
  <DropdownItem to="/projects">Edit Profile</DropdownItem>
  <DropdownItem to="/projects">Logout</DropdownItem>
</Dropdown>

dropdown.js

import React, { Component } from 'react'
import styled, { keyframes } from 'styled-components'
import { Link } from 'react-router'

const fadeInDown = keyframes`
  from {
    opacity: 0;
    transform: translateY(-5px);
  }

  to {
    opacity: 1;
    transform: translateY(0px);
  }
`

const Container = styled.div`
  background: #FFFFFF;
  border: 1px solid #E9ECF0;
  box-shadow: 0 0 15px 0 rgba(171,179,183,0.31);
  border-radius: 8px;
  padding: 15px;
  width: 160px;
  margin: 15px auto 0;
  position: relative;
  display: none;
  animation: ${fadeInDown} 0.1s linear;
  display: ${props => props.open ? 'block' : 'none'};

  &:after {
    position: absolute;
    left: 50%;
    top: -15px;
    margin-left: -15px;
    width: 0;
    height: 0;
    content: '';
    border-left: 15px solid transparent;
    border-right: 15px solid transparent;
    border-bottom: 15px solid rgb(255, 255, 255);
    filter: drop-shadow(0 1px 15px rgba(171,179,183,0.31));
    z-index: 1;
  }
`

export const DropdownItem = styled(Link)`
  color: rgba(68, 70, 76, 1);
  margin-bottom: 5px;
  padding: 10px 5px;
  display: block;

  &:hover {
    background-color: rgba(235, 100, 39, 0.1);
    color: rgba(235, 100, 39, 1);
    border-radius: 8px;
    cursor: pointer;
  }

  &:last-child {
    margin-bottom: 0;
  }
`

export default class Dropdown extends Component {
  constructor(props) {
    super(props);
    this.state = {
      isOpen: true
    }
  }

  toggle = (e) => {
    this.setState({
      isOpen: !this.state.isOpen
    });
  }

  collapse = (e) => {
    const { container } = this.refs;
    const { target } = event;

    if (!container.contains(target)) {
      this.setState({
        isOpen: false
      });
    }
  }

  componentDidMount() {
    document.body.addEventListener('click', this.collapse);
  }

  componentWillUnmount() {
    document.body.removeEventListener('click', this.collapse);
  }

  render() {
    const { isOpen } = this.state;
    const { children } = this.props;

    return (
      <div ref="container" tabIndex={0}>
        <button onClick={this.toggle}>Button</button>

        <Container open={isOpen} onBlur={this.collapse}>
          {children}
        </Container>
      </div>
    );
  }
}