Improve pre-publish panel styling (#7879)

* Use clearer wording for pre-publish panel prompt; fixes #7873.
* Style pre-publish panel more consistently with settings sidebar; fixes #7878.
* Switch to an all-white background for prepublish panel.

packages/editor/src/components/post-publish-panel/prepublish.js

@@ -26,7 +26,7 @@ function PostPublishPanelPrepublish( {
 	return (
 		<div className="editor-post-publish-panel__prepublish">
 			<div><strong>{ hasPublishAction ? __( 'Are you ready to publish?' ) : __( 'Are you ready to submit for review?' ) }</strong></div>
-			<p>{ hasPublishAction ? __( 'Here, you can do a last-minute check up of your settings below, before you publish.' ) : __( 'When you’re ready, submit your work for review, and an Editor will be able to approve it for you.' ) }</p>
+			<p>{ hasPublishAction ? __( 'Double-check your settings, then use the button to publish your post.' ) : __( 'When you’re ready, submit your work for review, and an Editor will be able to approve it for you.' ) }</p>
 			{ hasPublishAction && (
 				<Fragment>
 					<PanelBody initialOpen={ false } title={ [

packages/editor/src/components/post-publish-panel/style.scss

@@ -12,6 +12,7 @@
 }
 
 .editor-post-publish-panel__header {
+	background: $white;
 	padding-left: 16px;
 	height: $header-height;
 	border-bottom: $border-width solid $light-gray-500;
@@ -44,23 +45,22 @@
 
 .editor-post-publish-panel__link {
 	color: $blue-medium-700;
+	font-weight: 400;
 	padding-left: 4px;
 	text-decoration: underline;
 }
 
 .editor-post-publish-panel__prepublish {
 	padding: 16px;
 
+	strong {
+		color: $dark-gray-900;
+	}
+
 	.components-panel__body {
+		background: $white;
 		margin-left: -16px;
 		margin-right: -16px;
-		margin-bottom: -16px;
-		margin-top: 10px;
-		border: none;
-
-		.components-panel__body-toggle {
-			font-weight: 400;
-		}
 	}
 
 	.editor-post-visibility__dialog-legend {