A small adaptation to an already existing javascript

The existing javascript is an already existing and fully functioning product (a cookie privacy solution that keeps track of the user's consent to the use of cookies via a cookie) that you can view at [login to view URL] I would provide the freelancer with the existing .js file, CSS file, jQuery library and the script to be included in each htm file of my site. The script can already be customised in a number of ways and, in particular, you can have the widget open on 9 different positions (every combination of top, bottom and center with left, right and center). Als, the text inside the widget can be customised. Now my problem is that I need to have one position and text for desktop computers/tablets and a different position and text for smartphones. Specifically I'd like to have TOP-RIGHT position with a longer text for desktop/tablets and TOP-CENTER position with a shorter text for smartphones. At the moment whatever position and text I choose goes for both. So ideally I'd like to have two blocks of customisation code whose parameters are absolutely the same but that I could set separately, one for desktop/tablets pcs and one for smartphones. I had thought that you could set a IF... THEN condition in the CSS file (example: if the screen is more than 400px wide, use customisation block A, if it is less than 400px wide use customisation block B) but I have been told that CSS doesn't allow that and you'd have to do it using javascript. I am available online for answering questions about this task. Thank you.