Align .mw-ui-pressed to OOUI's active button state

Aligning `.mw-ui-pressed`, which is only available in ULS
to OOUI's active button state. It features an Accent10 blue border
for a cleaner appearance.

Change-Id: I147547cab74de2d84fb88d6e232b08fc8c4f4907

resources/css/ext.uls.languagesettings.less

@@ -123,6 +123,7 @@
 #languagesettings-panels .mw-ui-pressed {
 	background-color: #2a4b8d;
 	color: #fff;
+	border-color: #2a4b8d;
 }
 
 .checkbox input[type='checkbox'] {