Use Bootstrap 4

.\src\components\app.js

import { h, Component } from "preact";
import { Router } from "preact-router";

import Header from "./header";
import Home from "../routes/home";
import Movies from "../routes/movies";

export default class App extends Component {
  /** Gets fired when the route changes.
	 *	@param {Object} event		"change" event from [preact-router](http://git.io/preact-router)
	 *	@param {string} event.url	The newly routed URL
	 */
  handleRoute = e => {
    this.currentUrl = e.url;
  };

  render() {
    return (
      <div id="app" class="container">
        <Header />
        <Router onChange={this.handleRoute}>
          <Home path="/" />
          <Movies path="/movies" />
        </Router>
      </div>
    );
  }
}

.\src\index.js

import "bootstrap/dist/css/bootstrap.min.css";
import App from "./components/app";

export default App;

npm-install.ps1

npm install bootstrap