Administration: Improve the usage of the button CSS classes.

Introduces some consistency in the usage of the button CSS classes, fixes the
focus style for accessibility and responsiveness of the buttons.

- Adds the `button` class to all primary buttons make them responsive
- Removes all `secondary-button` classes and replaces it with button when needed. `button-secondary` shouldn't be used and exists just for backward compatibility reasons
- Replaces classes inside `submit_button()` with a shorthand for some buttons, and use an empty string for the default `button` class. Passing `button` is unnecessary
- Adjusts `get_submit_button()` to remove empty items

Props iseulde, dimchik, chris_d2d, mhowell, afercia.
Fixes #27314, #37138, #37448.


git-svn-id: https://develop.svn.wordpress.org/trunk@38672 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/js/customize-widgets.js

@@ -835,7 +835,7 @@
 			$saveBtn = this.container.find( '.widget-control-save' );
 			$saveBtn.val( l10n.saveBtnLabel );
 			$saveBtn.attr( 'title', l10n.saveBtnTooltip );
-			$saveBtn.removeClass( 'button-primary' ).addClass( 'button-secondary' );
+			$saveBtn.removeClass( 'button-primary' );
 			$saveBtn.on( 'click', function( e ) {
 				e.preventDefault();
 				self.updateWidget( { disable_form: true } ); // @todo disable_form is unused?

src/wp-admin/js/updates.js

@@ -1105,7 +1105,7 @@
 				$message.siblings( '.preview' ).replaceWith( function () {
 					return $( '<a>' )
 						.attr( 'href', response.customizeUrl )
-						.addClass( 'button button-secondary load-customize' )
+						.addClass( 'button load-customize' )
 						.text( wp.updates.l10n.livePreview );
 				} );
 			}

src/wp-admin/js/widgets.js

@@ -354,12 +354,12 @@ wpWidgets = {
 			if ( $target.hasClass('button-primary') ) {
 				self.addWidget( chooser );
 				self.closeChooser();
-			} else if ( $target.hasClass('button-secondary') ) {
+			} else if ( $target.hasClass( 'widgets-chooser-cancel' ) ) {
 				self.closeChooser();
 			}
 		}).on( 'keyup.widgets-chooser', function( event ) {
 			if ( event.which === $.ui.keyCode.ENTER ) {
-				if ( $( event.target ).hasClass('button-secondary') ) {
+				if ( $( event.target ).hasClass( 'widgets-chooser-cancel' ) ) {
 					// Close instead of adding when pressing Enter on the Cancel button
 					self.closeChooser();
 				} else {