product responsive

Okay so I think you found it difficult to do the responsive design because you used the same image for both desktop and mobile. There where two separate images so to achieve a responsive design you had to use a picture tag instead of the image tag you used.

For example this:

<img src="images/image-product-desktop.jpg" alt="">

would replaced by this:

<picture>
  <source media="(max-width:600px)" srcset="images/image-product-mobile.jpg"/>
  <img src="images/image-product-desktop.jpg" alt="" />
</picture>

You can find more information at this link.

Hope this helps.