DON-1065: Add white background to main-menu submenus when opened via …

…click

Affects mainly wide touch-screen devices such as tablets or horizontal
phones. Currently in prod these can't open the menu at all, and in
staging the menu opens but has a transparent background so is not
readable.

src/components/biggive-main-menu/biggive-main-menu.scss

@@ -433,6 +433,11 @@ nav {
   display: block !important;
 }
 
+#nav-primary .display-sub-menu, #nav-primary .display-sub-menu li {
+  background-color: white;
+}
+
+
 .sub-menu-main {
   position: absolute;
   top: $upper-nav-height-desktop;