Admin: Set info notices to use white background.

The admin reskin changed info notices to a transparent background, matching usage in Gutenberg. But with the gray background in the core admin, these notices didn't show up in an expected manner. Additionally, using a transparent background in a context where the background color is variable is risky for color contrast.

Change `.notice-info`, `.notice-info.notice-alt`, and `.login .notice, .login .message` to use white backgrounds. Reverts changes from [61731] to apply styles also to `.message` class.

Props mohitbsf, audrasjb, peterwilsoncc, pbiron, fabiankaegy, noruzzaman, joedolson.
Fixes #64678. See #64715.

git-svn-id: https://develop.svn.wordpress.org/trunk@61737 602fd350-edb4-49c9-b593-d223f7449a82

Author: joedolson

src/wp-admin/css/common.css

@@ -1575,11 +1575,11 @@ div.error.notice-alt {
 
 .notice-info {
 	border-left-color: #3858e9;
-	background-color: transparent;
+	background-color: #fff;
 }
 
 .notice-info.notice-alt {
-	background-color: transparent;
+	background-color: #fff;
 }
 
 #plugin-information-footer .update-now:not(.button-disabled):before {

src/wp-admin/css/login.css

@@ -49,7 +49,7 @@ p {
 	margin-top: 0;
 	margin-left: 0;
 	margin-bottom: 20px;
-	background-color: transparent;
+	background-color: #fff;
 	word-wrap: break-word;
 }
 
@@ -66,10 +66,6 @@ p {
 	background-color: #eff9f1;
 }
 
-.login .notice {
-	background-color: #fff;
-}
-
 /* Match border color from common.css */
 .login .notice-error {
 	border-left-color: #cc1818;