Show nav shortcut only on devices smaller than 990px

www/solar/ui.css

@@ -151,7 +151,7 @@ blockquote {
 	left: 10px;
 }
 
-@media (max-width: 1200px) {
+@media (max-width: 990px) {
 	.mobile-nav {
 		display: block;
 	}