diff -r 3d4e9c994f10 -r a86126ab1dd4 wp/wp-includes/js/tinymce/plugins/compat3x/css/dialog.css
--- a/wp/wp-includes/js/tinymce/plugins/compat3x/css/dialog.css	Tue Oct 22 16:11:46 2019 +0200
+++ b/wp/wp-includes/js/tinymce/plugins/compat3x/css/dialog.css	Tue Dec 15 13:49:49 2020 +0100
@@ -1,3 +1,8 @@
+/*
+ * Edited for compatibility with old TinyMCE 3.x plugins in WordPress.
+ * More info: https://core.trac.wordpress.org/ticket/31596#comment:10
+ */
+
 /* Generic */
 body {
 font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen-Sans, Ubuntu, Cantarell, "Helvetica Neue", sans-serif;