Accessibility: Improve and modernize user interface controls for better contrast. Second part: tables, meta boxes, and other user interface elements.

Introduces better contrast for borders of the following user interface elements:
- Tables
- Screen Options and Help 
- Admin notices
- Welcome panel
- Meta boxes (post boxes)
- Cards
- Health Check accordions and headings
- Theme and Plugin upload forms

Props kjellr, melchoyce, karmatosed, audrasjb.
Fixes #48101.

Built from https://develop.svn.wordpress.org/trunk@46242


git-svn-id: http://core.svn.wordpress.org/trunk@46054 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/css/edit.css

@@ -153,7 +153,7 @@ body.post-new-php .submitbox .submitdelete {
 .postbox {
 	position: relative;
 	min-width: 255px;
-	border: 1px solid #e5e5e5;
+	border: 1px solid #ccd0d4;
 	box-shadow: 0 1px 1px rgba(0, 0, 0, 0.04);
 	background: #fff;
 }
@@ -309,7 +309,7 @@ form#tags-filter {
 #post-status-info {
 	width: 100%;
 	border-spacing: 0;
-	border: 1px solid #e5e5e5;
+	border: 1px solid #ccd0d4;
 	border-top: none;
 	background-color: #f7f7f7;
 	box-shadow: 0 1px 1px rgba(0, 0, 0, 0.04);
@@ -360,7 +360,7 @@ form#tags-filter {
 
 .wp-editor-expand #wp-content-editor-tools {
 	z-index: 1000;
-	border-bottom: 1px solid #e5e5e5;
+	border-bottom: 1px solid #ccd0d4;
 }
 
 .wp-editor-expand #wp-content-editor-container {
@@ -377,7 +377,7 @@ form#tags-filter {
 }
 
 .wp-editor-expand #post-status-info {
-	border-top: 1px solid #e5e5e5;
+	border-top: 1px solid #ccd0d4;
 }
 
 .wp-editor-expand div.mce-toolbar-grp {