Make Google Fonts @import protocol-relative.

static/main.css

@@ -1,4 +1,4 @@
-@import url(http://fonts.googleapis.com/css?family=Open+Sans:400,400italic,700|Oxygen:700);
+@import url(//fonts.googleapis.com/css?family=Open+Sans:400,400italic,700|Oxygen:700);
 
 body {
     margin: 0;