Big Cartel Luna Theme: How to update code for prices to display on mobile differently from desktop

Question

There is a product list info option to set for the theme. I want to use "under image" for the mobile setting and "on rollover" for the desktop setting. Where and how can I set this in the HTML code? Through the account design settings front-end the option applies for both environments. Thanks for your help!

I looked in the CSS file to find code that I thought I could modify and didn't find anything... I am not a web designer, just have light knowledge.