Hi,
Our Templates don't touch the invoice layout, email templates and order details layouts (because they are frequently updated by Virtuemart developers in every single virtuemart release).
See the PHP files in these folders to re-style those layouts if you want to:
/components/com_virtuemart/views/invoice/tmpl/
/components/com_virtuemart/views/orders/tmpl/
You should better use "template overriding" to make any changes in those files. Because if you don't and update your Virtuemart to any newer version, your changes will be retrieved back to original state.
Check these articles for more information about template overriding:
www.ostraining.com/blog/joomla/overrides/
docs.joomla.org/How_to_override_the_output_from_the_Joomla!_core
Regards.