Themes: Set a max-width on screenshots so they don't get blurry at very wide screen widths.

props matveb.
fixes #26172.

Built from https://develop.svn.wordpress.org/trunk@26730


git-svn-id: http://core.svn.wordpress.org/trunk@26619 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/css/wp-admin-rtl.css

@@ -6865,6 +6865,7 @@ body.folded .theme-overlay .theme-wrap {
 	float: right;
 	margin: 0 0 0 30px;
 	width: 55%;
+	max-width: 880px;
 	text-align: center;
 }
 

wp-admin/css/wp-admin.css

@@ -6865,6 +6865,7 @@ body.folded .theme-overlay .theme-wrap {
 	float: left;
 	margin: 0 30px 0 0;
 	width: 55%;
+	max-width: 880px;
 	text-align: center;
 }