Notices: Add styles for use against white backgrounds.

These colored backgrounds can be accessed by adding the `.notice-alt` class to a notice.

There is also now a large version when using the `.notice-large` class, and a `.notice-title` class that is appropriate for headline text within a large notice.

props paulwilde, hugobaeta, melchoyce.
fixes #32244.

Built from https://develop.svn.wordpress.org/trunk@34365


git-svn-id: http://core.svn.wordpress.org/trunk@34329 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/css/themes.css

@@ -786,24 +786,6 @@ body.folded .theme-overlay .theme-wrap {
 	margin-right: 5px;
 }
 
-/* Theme Updates info */
-.theme-overlay .theme-update-message {
-	background: #fef7f1;
-	border: 1px solid #eee;
-	border-left: 4px solid #d54e21;
-	-webkit-border-radius: 3px;
-	border-radius: 3px;
-	padding: 5px 20px 10px;
-}
-
-.theme-overlay .theme-update {
-	color: #23282d;
-	font-size: 18px;
-	display: inline-block;
-	line-height: 40px;
-	margin: 0;
-}
-
 .theme-overlay .parent-theme {
 	background: #f7fcfe;
 	border: 1px solid #eee;