I am using sharepoint 2013 on premise.
I am working on an interesting project where we have created re-usable branding by separating color.css and all other css. For each site collection, 3 css files are same and 1 css file is different.
So, when I have some improvements in one of the three css that are common to all site collections, I have to go and update then in style library/en-us/themable folder of all site collections.
Is there any easy way to resolve this other than maintaining wsp package?
-- Updates --
I know there are two solutions in my case, either I need to create wsp, or powershell to copy it over to different locations. I want to know if there is any other way to do this in shareopint 2013, may be cross site collection publishing or any new feature?
Thank you all for the response