Admin: Fix alignment of dashboard widgets and welcome panel.

Adjust padding and margins of dashboard widgets to properly align with the content width, matching the Welcome Panel.

Props marc4, hbhalodia, noruzzaman, soyebsalar01, joedolson.
Fixes #64739.

git-svn-id: https://develop.svn.wordpress.org/trunk@61759 602fd350-edb4-49c9-b593-d223f7449a82

Author: joedolson

src/wp-admin/css/dashboard.css

@@ -40,7 +40,7 @@
 
 #dashboard-widgets-wrap {
 	overflow: hidden;
-	margin: 0 -4px;
+	margin: 0 -8px;
 }
 
 #dashboard-widgets .postbox {
@@ -59,8 +59,8 @@
 	display: flow-root; /* avoid margin collapsing between parent and first/last child elements */
 	/* Required min-height to make the jQuery UI Sortable drop zone work. */
 	min-height: 0;
-	margin-right: 8px;
-	padding: 4px;
+	margin: 0 8px 20px;
+	padding: 0;
 }
 
 #dashboard-widgets .meta-box-sortables:not(:empty) {