load external css file attach to menu item type

-- HikaShop version -- : 2.6.4
-- Joomla version -- : 3.6.2
-- PHP version -- : 5.5

Hi
For see in the client side Front End a list of product ; is there a way in the backend GUI to configure hikashop load a specific css file when click in frontEnd on a hikashop menu item .
I don't want to change the structure of html code ( by choose a php template like listing_list.php ....) only select ( attach) with this php file a css file that ll be load in in the client side for override the others styles !!

Regard's

I know this documentation and which php code to use for insert css file . I was thinking there was a backend GUI way to add this using joomla or hikashop . It very strange to see how we can style in joomla !
By default We could only add new selector and css code in css file refer to suffix prefix chrome concept but never load custom css file even in menu item type " component content".
The only availablechoice to have a new style in menu item type is to select a new entire template Style !!!

hope this ll change soon ...

for information to dev that need this functionnalities .
there is a module that can be load refer to active menu tiem type . This module insert css content ( paste css content or external css file) .
see www.hyde-design.co.uk/free-joomla-extensions/custom-css