Update main.css to use GG blue (#33)

Author: pierrelalanne

media/main.css

@@ -22,12 +22,12 @@ p {
 }
 
 button.large {
-    background-color: #2200fb;
+    background-color: #1b2d55;
     color: white;
     border: none;
     padding: 10px 20px;
     font-size: 16px;
     cursor: pointer;
     border-radius: 5px;
     margin: 2em 0;
-}
+}