Different CSS style depending on document type

Hello,

I am trying to use different CSS files depending on document type, for example if document is an invoice it will use “style_invoice.css” but for packing slips it will use “style_packing.css”.

I know it can be possible with snippets, but I want to code it within template files.

So in my template folder, inside “html-document-wrapper.php” file I have removed this line :

<style type="text/css"><?php $this->template_styles(); ?></style>

and added instead :

<?php if ($template_type == 'invoice') { ?>
	<style type="text/css"><?php include './style_invoice.css'; ?></style>
<?php } ?>

But this do not work, any idea how to achieve this ?

Thanks for your help.