How to use a random css in JavaScript?

I'm having problems trying to figure this out, specifically because I'm really new to java. So, I have this place in my page where I want to have a random css file that I will make in css and I will like to link to it. I want it to be randomized every time the page refreshes, because I will do lots of these css files.

So, is this possible? I've searched for answers but all of the randomized css questions I've found are about the whole page. I just want a little part of the page to be randomized, similar to the random image I have in the same webpage.

The page I'm using for testing is this one: http://ift.tt/1V3g1OL , I would like to use the toggle that says "búsquedas" for this. So, any help? thanks and exuse my poor english!