Make broadcast message look like a warning by default

app/assets/stylesheets/generic/common.scss

@@ -306,18 +306,6 @@ table {
   width: 100%;
 }
 
-.broadcast-message {
-  padding: 10px;
-  text-align: center;
-  background: #555;
-  color: #BBB;
-}
-
-.broadcast-message-preview {
-  @extend .broadcast-message;
-  margin-bottom: 20px;
-}
-
 .btn-sign-in {
   margin-top: 5px;
   text-shadow: none;

app/assets/stylesheets/pages/admin.scss

@@ -50,3 +50,14 @@
     line-height: 2;
   }
 }
+
+.broadcast-message {
+  @extend .alert-warning;
+  padding: 10px;
+  text-align: center;
+}
+
+.broadcast-message-preview {
+  @extend .broadcast-message;
+  margin-bottom: 20px;
+}