TinyMCE: fix the styling of notices generated by the editor UI.

Props: mor10, karmatosed, azaozz.
Fixes #38917 for 4.7.

git-svn-id: https://develop.svn.wordpress.org/branches/4.7@39501 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/css/editor.css

@@ -858,6 +858,11 @@ div.mce-menu .mce-menu-item-sep,
 	border-left-color: #23282d;
 }
 
+div.mce-notification {
+	left: 10% !important;
+	right: 10%;
+}
+
 .mce-notification button.mce-close {
 	right: 6px;
 	top: 3px;