Problem to get linked CSS file used by the Editor

I have a rather complicated template in use for http://www.hoveniersbedrijf-timmerman.nl/_new_site/ and I was the "mid section" to be edited by the customer.

The mid-section is loaded by a PHP INCLUDE and by itself it is a table of three rows and two columns.
In the 2nd row, first colomn (with rowspan = 2) there is the editable text marked with the snippets tags.
Please view the sourcecode of http://www.hoveniersbedrijf-timmerman.nl/_new_site/welkom_mid.php
This page by itself has been given the linked CSS because you can see how it should look like.

Trying to edit this text I cann't get the linked css included in the editor, which confuses when editing.
This despite it has been defined in the parent and the child page.

Anyone solved this issue??