added error pages and further styling

public/index.html

@@ -11,6 +11,7 @@
   <!-- Compiled and minified CSS -->
   <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/materialize/1.0.0/css/materialize.min.css">
   <link rel="manifest" href="%PUBLIC_URL%/manifest.json" />
+  <link href="https://fonts.googleapis.com/icon?family=Material+Icons" rel="stylesheet">
 
   <title>React App</title>
 </head>