blur content when the menu is open

_layouts/default.html

@@ -7,7 +7,7 @@ layout: compress
 
 <body data-theme="{{ site.mode }}">
   {% include navbar.html %}
-  <div class="wrapper">
+  <div class="wrapper" id="wrapper">
     {% include author.html %}
     <main aria-label="Content">
       {{ content }}
@@ -15,4 +15,4 @@ layout: compress
     {% include footer.html %}
   </div>
 </body>
-</html>
+</html>