Admin: Update button color to align with the design system.

Updates the disabled state colors for the primary and secondary buttons to align with the WordPress Design System.

Props hbhalodia, huzaifaalmesbah, Joen, mciampini, ozgursar, wildworks.
Fixes #64797.

git-svn-id: https://develop.svn.wordpress.org/trunk@61840 602fd350-edb4-49c9-b593-d223f7449a82

Author: t-hamano

src/wp-includes/css/buttons.css

@@ -208,8 +208,8 @@ TABLE OF CONTENTS:
 .wp-core-ui .button-secondary:disabled,
 .wp-core-ui .button-secondary.disabled,
 .wp-core-ui .button-disabled {
-	color: #949494 !important;
-	border-color: #dddddd !important;
+	color: #8a8a8a !important;
+	border-color: #d8d8d8 !important;
 	background: transparent !important;
 	box-shadow: none !important;
 	cursor: default;
@@ -312,9 +312,9 @@ TABLE OF CONTENTS:
 .wp-core-ui .button-primary:disabled,
 .wp-core-ui .button-primary-disabled,
 .wp-core-ui .button-primary.disabled {
-	color: #949494 !important;
-	background: #f0f0f0 !important;
-	border-color: #f0f0f0 !important;
+	color: #8a8a8a !important;
+	background: #e2e2e2 !important;
+	border-color: #e2e2e2 !important;
 	box-shadow: none !important;
 	text-shadow: none !important;
 	cursor: default;