Fix Macaron theme

The modal for reporting a post calculates its value based on $ui-secondary-color. In most themes that is the correct calculation to make, but in Macaron our colors are assigned a little differently and this makes the modal unusable. Setting it to white fixes the issue.

app/javascript/styles/macaron/diff.scss

@@ -1095,3 +1095,7 @@ a.status-card.compact:hover {
 .audio-player .video-player__time-total {
   color: $ui-primary-color;
 }
+
+.report-dialog-modal {
+  background: $white;
+}