petersch wrote: didnt work
Yup, I know. Nothing with CSS only seems to work. Think it's a "misunderstanding" of what your template on one hand and HikaShop on the other use for "responsiveness". Not that it must be relevant in this case, but had (other) trouble with Gantry templates before. I'm just saying this for you to understand that I stopped using them and am not familiar with them anymore. You should still be able to have your images responsive just as elsewhere on your site.
Anyhow, to me it looks as if it'll take a different approach with layout-relevant code in the views (where the product slider is a case by itself) to achieve responsiveness. Again, elsewhere on your site CSS for images with only max-width:100% and height:auto works, so it should be possible to make it work for images in HikaShop as well. But it might require altering at least some of the size settings in views...