Change drawer type from dismissable to modal

luhn-algorithm/index.html

@@ -43,7 +43,7 @@
     </head>
     <body>
         <!-- content of navbar is included via jQuery -->
-        <aside class="navbar-insert mdc-drawer mdc-drawer--dismissible"></aside>
+        <aside class="navbar-insert mdc-drawer mdc-drawer--modal"></aside>
 
         <div class="mdc-drawer-app-content">
             <header class="mdc-top-app-bar app-bar" id="app-bar">