React-不显示路由器子路由

import React from 'react';
import { BrowserRouter as Router, Route, Switch, Link } from 'react-router-dom';

function App() {
  return (
    <Router>
      <div>
        <nav>
          <ul>
            <li>
              <Link to="/dashboard">Dashboard</Link>
            </li>
          </ul>
        </nav>

        <Switch>
          <Route path="/dashboard" component={Dashboard} />
        </Switch>
      </div>
    </Router>
  );
}

function Dashboard() {
  return (
    <div>
      <h2>Dashboard</h2>
      <nav>
        <ul>
          <li>
            <Link to="/dashboard/profile">Profile</Link>
          </li>
          <li>
            <Link to="/dashboard/settings">Settings</Link>
          </li>
        </ul>
      </nav>

      <Switch>
        <Route path="/dashboard/profile" component={Profile} />
        <Route path="/dashboard/settings" component={Settings} />
      </Switch>
    </div>
  );
}

function Profile() {
  return <h3>Profile</h3>;
}

function Settings() {
  return <h3>Settings</h3>;
}

export default App;