剛開始的代碼是這樣的，使用react router4.x寫的demo路由跳轉后，頁面的沒有渲染，是因為沒有引入外部css文件（或者說引入外部文件路徑錯誤）
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<meta name="theme-color" content="#000000">
<link rel="manifest" href="%PUBLIC_URL%/manifest.json">
<title>React App</title>
<link rel="stylesheet" href="./css/bootstrap.css">
</head>
<body>
<noscript>
You need to enable JavaScript to run this app.
</noscript>
<div id="root"></div>
</body>
</html>
將上面代碼（紅色部分）的點去掉就可以了，如下所示
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<meta name="theme-color" content="#000000">
<link rel="manifest" href="%PUBLIC_URL%/manifest.json">
<title>React App</title>
<link rel="stylesheet" href="/css/bootstrap.css">
</head>
<body>
<noscript>
You need to enable JavaScript to run this app.
</noscript>
<div id="root"></div>
</body>
</html>