The register tags that you have copied apply to the live demos of RadControls only and they are not used by the RadEditor's dialogs.
The header in the Link manager is created by a table and RadTabStrip.
The OK and Cancel buttons in the bottom of the dialog are styled by RadFormDecorator
If you would like you can inspect the contents of the different dialogs by registering the external dialogs of RadEditor as shown in the following demo: Customize Built-in Dialogs
. The dialog files are located in the EditorDialogs installation folder.
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed