Fix missing colon in empty.css

assets/css/empty.css

@@ -11,6 +11,6 @@
 
 @media screen and (max-width: 1500px) and (max-height: 1000px) {
     #logo > h1 {
-      font-size 10vmin;
+      font-size: 10vmin;
     }
 }