Gallery Widget: Remove grey background behind gallery, and align images to the edge of the container.

Props Presskopp, benoitchantre, mrasharirfan.
Fixes #42101.

Built from https://develop.svn.wordpress.org/trunk@41833


git-svn-id: http://core.svn.wordpress.org/trunk@41667 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/css/widgets-rtl.css

@@ -96,7 +96,7 @@
 }
 
 .media-widget-control .media-widget-preview {
-	background: #f1f1f1;
+	background: transparent;
 	text-align: center;
 }
 .media-widget-control .media-widget-preview .notice {
@@ -168,6 +168,7 @@
 	-webkit-box-pack: start;
 	justify-content: flex-start;
 	flex-wrap: wrap;
+	margin: -1.79104477%;
 }
 
 .media-widget-preview.media_gallery,
@@ -175,11 +176,18 @@
 	cursor: pointer;
 }
 
+.media-widget-preview.media_image,
+.media-widget-preview.media_audio,
+.attachment-media-view {
+	background: #f1f1f1;
+}
+
 .media-widget-gallery-preview .gallery-item {
 	box-sizing: border-box;
 	width: 50%;
 	margin: 0;
 	padding: 1.79104477%;
+	background: transparent;
 }
 
 /*

wp-admin/css/widgets.css

@@ -96,7 +96,7 @@
 }
 
 .media-widget-control .media-widget-preview {
-	background: #f1f1f1;
+	background: transparent;
 	text-align: center;
 }
 .media-widget-control .media-widget-preview .notice {
@@ -168,6 +168,7 @@
 	-webkit-box-pack: start;
 	justify-content: flex-start;
 	flex-wrap: wrap;
+	margin: -1.79104477%;
 }
 
 .media-widget-preview.media_gallery,
@@ -175,11 +176,18 @@
 	cursor: pointer;
 }
 
+.media-widget-preview.media_image,
+.media-widget-preview.media_audio,
+.attachment-media-view {
+	background: #f1f1f1;
+}
+
 .media-widget-gallery-preview .gallery-item {
 	box-sizing: border-box;
 	width: 50%;
 	margin: 0;
 	padding: 1.79104477%;
+	background: transparent;
 }
 
 /*

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.9-beta1-41832';
+$wp_version = '4.9-beta1-41833';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.