How to build a custom Sidebar Component in React

import React from 'react';
import ReactDOM from 'react-dom';
import { IndexLink, Link } from 'react-router';
import './Sidebar.scss';
import classNames from 'classnames';

class Sidebar extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      showMenu: false,
    };
    this.toggleMenu = this.toggleMenu.bind(this);
  }
  componentDidMount() {
    document.addEventListener(
      'click',
      this.handleClickOutside.bind(this),
      true
    );
  }

  componentWillUnmount() {
    document.removeEventListener(
      'click',
      this.handleClickOutside.bind(this),
      true
    );
  }
  toggleMenu() {
    this.setState({ showMenu: !this.state.showMenu });
  }
  handleClickOutside(event) {
    const domNode = ReactDOM.findDOMNode(this);

    if (!domNode || !domNode.contains(event.target)) {
      this.setState({
        showMenu: false,
      });
    }
  }

  render() {
    const showMenu = this.state.showMenu;
    const sidebarClass = classNames({
      sidebar: true,
      'sidebar-menu-expanded': showMenu,
      'sidebar-menu-collapsed': !showMenu,
    });

    const elementsClass = classNames({
      'expanded-element': true,
      'is-hidden': !showMenu,
    });

    return (
      <nav className={sidebarClass}>
        <img className="menuIcon" src={menuIcon} onClick={this.toggleMenu} />
        <ul>
          <li>
            <Link className="expandable" to="/setting" title="Setting">
              <img src={'https://png.icons8.com/setting/ffffff'} alt="" />
              <span className={elementsClass}>Setting</span>
            </Link>
          </li>
        </ul>
      </nav>
    );
  }
}

export default Sidebar;

// Sidebar.scss
.menuIcon {
  margin-top: 70px;
  cursor: pointer;
}
nav.sidebar-menu-collapsed {
  width: 70px;
}

nav.sidebar-menu-expanded {
  width: 211px;
  z-index: 1;
}

nav.sidebar {
  position: fixed;
  top: 0px;
  left: 0px;
  height: 100%;
  background: none repeat scroll 0 0 #000000;
  color: white;
  padding: 20px 10px;
}

nav.sidebar a#justify-icon {
  outline: 0;
  color: white;
  font-size: 24px;
  font-style: normal;
}

nav.sidebar ul {
  margin: 0;
  padding: 0;
  // margin-top: 60px;
}

nav.sidebar ul li {
  margin: 0;
  padding: 0;
  margin-top: 20px;
  list-style-type: none;
}

nav.sidebar ul li a.expandable {
  outline: 0;
  color: white;
  text-decoration: none;
  font-size: 20px;
}

nav.sidebar ul li a.expandable:hover {
  color: #bbbbbb;
}

nav.sidebar ul li a.expandable span.expanded-element {
  color: #fff;
  margin-left: 12px;
  // display: none;
  font-size: 16px;
  position: relative;
  bottom: 2px;
}

nav.sidebar ul li.active {
  background: none repeat scroll 0 0 black;
  border-radius: 4px;
  text-align: center;
  margin-left: -4px;
  padding: 4px;
}

nav.sidebar ul li.active a.expandable {
  color: white !important;
}

nav.sidebar ul li.active a.expandable:hover {
  color: white !important;
}