add inline-code grey background

So much grey! All the grey's!

docs/index.html

@@ -34,6 +34,9 @@
       .small .remark-code { font-size: 16px; }
 
       .remark-code, .remark-inline-code { font-family: 'Ubuntu Mono'; }
+      .remark-inline-code {
+         background-color: #ccc;
+     }
       .red { color: #fa0000; }
       .gray { color: #ccc; }
       .small { font-size: 70%; }