Pages with only forms should take up entire page

On Special:MobileOptions we want to make the form take up the full
width but pad the fields in the form
(per https://phabricator.wikimedia.org/T180095#3795514)

This change is harmless but is necessary as soon as we port
the page to OOjs UI (I70f68df9d2d305126444319b05675702af75de87)

Bug: T180095
Change-Id: I1dda3eb4d0e7ebbec544dc0f5763b079e38f5cc8

resources/skins.minerva.base.styles/ui.less

@@ -444,6 +444,8 @@ input.search {
 .backtotop,
 .image-list,
 .pre-content,
+// Form only pages e.g Special:MobileOptions
+#mw-content-text > form .oo-ui-fieldLayout-body,
 .content,
 .post-content {
 	margin: 0 @contentMargin;

resources/skins.minerva.tablet.styles/common.less

@@ -56,6 +56,8 @@ A file for css that optimises the Minerva skin on larger devices.
 
 	// FIXME: Have a class that identifies all of these selectors
 	.pre-content,
+	// Form only pages e.g. Special:MobileOptions
+	#mw-content-text > form,
 	.content,
 	.post-content {
 		max-width: @contentMaxWidthTablet;
@@ -134,6 +136,10 @@ A file for css that optimises the Minerva skin on larger devices.
 	.content-unstyled,
 	.pre-content,
 	.post-content,
+	// Form only pages e.g. Special:MobileOptions
+	#mw-content-text > form,
+	// Form only pages e.g Special:MobileOptions
+	#mw-content-text > form .oo-ui-fieldLayout-body,
 	// FIXME: remove need for id selector
 	#mw-mf-page-center .pointer-overlay {
 		margin-left: auto;