React tutorial - css not loading

I'm working through a tutorial on React/Spring Boot located here. All was going well, including the initial display of groups on React.

However, once the React piece was refactored to separate the group list into a separate module and a nav bar was added, I get a display without any css rendering.

Here is the code:

App.js

import React, { Component } from 'react';
import './App.css';
import Home from './Home';
import { BrowserRouter as Router, Route, Switch } from 'react-router-dom';
import GroupList from './GroupList';

class App extends Component {
  render() {
    return (
      <Router>
        <Switch>
          <Route path='/' exact={true} component={Home}/>
          <Route path='/groups' exact={true} component={GroupList}/>
        </Switch>
      </Router>
    )
  }
}

export default App; 

AppNavbar.js

import React, { Component } from 'react';
import { Collapse, Nav, Navbar, NavbarBrand, NavbarToggler, NavItem, NavLink } from 'reactstrap';
import { Link } from 'react-router-dom';

export default class AppNavbar extends Component {
  constructor(props) {
    super(props);
    this.state = {isOpen: false};
    this.toggle = this.toggle.bind(this);
  }

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

  render() {
    return <Navbar color="dark" dark expand="md">
      <NavbarBrand tag={Link} to="/">Home</NavbarBrand>
      <NavbarToggler onClick={this.toggle}/>
      <Collapse isOpen={this.state.isOpen} navbar>
        <Nav className="ml-auto" navbar>
          <NavItem>
            <NavLink
              href="https://twitter.com/oktadev">@oktadev</NavLink>
          </NavItem>
          <NavItem>
            <NavLink href="https://github.com/oktadeveloper/okta-spring-boot-react-crud-example">GitHub</NavLink>
          </NavItem>
        </Nav>
      </Collapse>
    </Navbar>;
  }
}

Home.js

import './App.css';
import AppNavbar from './AppNavbar';
import { Link } from 'react-router-dom';
import { Button, Container } from 'reactstrap';

class Home extends Component {
  render() {
    return (
      <div>
        <AppNavbar/>
        <Container fluid>
          <Button color="link"><Link to="/groups">Manage JUG Tour</Link></Button>
        </Container>
      </div>
    );
  }
}

export default Home;

GroupList.js

import React, { Component } from 'react';
import { Button, ButtonGroup, Container, Table } from 'reactstrap';
import AppNavbar from './AppNavbar';
import { Link } from 'react-router-dom';

class GroupList extends Component {

  constructor(props) {
    super(props);
    this.state = {groups: [], isLoading: true};
    this.remove = this.remove.bind(this);
  }

  componentDidMount() {
    this.setState({isLoading: true});

    fetch('api/groups')
      .then(response => response.json())
      .then(data => this.setState({groups: data, isLoading: false}));
  }

  async remove(id) {
    await fetch(`/api/group/${id}`, {
      method: 'DELETE',
      headers: {
        'Accept': 'application/json',
        'Content-Type': 'application/json'
      }
    }).then(() => {
      let updatedGroups = [...this.state.groups].filter(i => i.id !== id);
      this.setState({groups: updatedGroups});
    });
  }

  render() {
    const {groups, isLoading} = this.state;

    if (isLoading) {
      return <p>Loading...</p>;
    }

    const groupList = groups.map(group => {
      const address = `${group.address || ''} ${group.city || ''} ${group.stateOrProvince || ''}`;
      return <tr key={group.id}>
        <td style={{whiteSpace: 'nowrap'}}>{group.name}</td>
        <td>{address}</td>
        <td>{group.events.map(event => {
          return <div key={event.id}>{new Intl.DateTimeFormat('en-US', {
            year: 'numeric',
            month: 'long',
            day: '2-digit'
          }).format(new Date(event.date))}: {event.title}</div>
        })}</td>
        <td>
          <ButtonGroup>
            <Button size="sm" color="primary" tag={Link} to={"/groups/" + group.id}>Edit</Button>
            <Button size="sm" color="danger" onClick={() => this.remove(group.id)}>Delete</Button>
          </ButtonGroup>
        </td>
      </tr>
    });

    return (
      <div>
        <AppNavbar/>
        <Container fluid>
          <div className="float-right">
            <Button color="success" tag={Link} to="/groups/new">Add Group</Button>
          </div>
          <h3>My JUG Tour</h3>
          <Table className="mt-4">
            <thead>
            <tr>
              <th width="20%">Name</th>
              <th width="20%">Location</th>
              <th>Events</th>
              <th width="10%">Actions</th>
            </tr>
            </thead>
            <tbody>
            {groupList}
            </tbody>
          </Table>
        </Container>
      </div>
    );
  }
}

export default GroupList;

App.css

.App {
  text-align: center;
}

.container, .container-fluid {
  margin-top: 20px;
}  

.App-logo {
  height: 40vmin;
  pointer-events: none;
}

@media (prefers-reduced-motion: no-preference) {
  .App-logo {
    animation: App-logo-spin infinite 20s linear;
  }
}

.App-header {
  background-color: #282c34;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  font-size: calc(10px + 2vmin);
  color: white;
}

.App-link {
  color: #61dafb;
}

@keyframes App-logo-spin {
  from {
    transform: rotate(0deg);
  }
  to {
    transform: rotate(360deg);
  }

}

Any help much appreciated.