Product Preview Card - Mobile First, Javascript, and Flexbox

I used Javascript to be able to change the source of the image instead of HTML srcset. I just wanted the practice of using javascript on a project! Id love any feedback on the format of my code, how I wrote my javascript code and included it in my HTML. My only question is that the product card is responsive in all the mobile options except when it goes below a width of 375px there seems to be some white space that shows below the main background. Any tips for why that is happening would be appreciated.