Problem: How to add more classes to product listing (modules/product_listing.php)

Solution: ?

I try to make fluid listing with background images, so I need more classes to get things done. At least one class is needed so I can use .productListing-odd, .productListing-even for left side of image and new class for right side. More extras gives more possibilities, but one would be enough.

And if this should be possible without extra classes i would be happy to see that solution too.

This has been so easy with other parts of Zencart, I'm pretty sure I'm missing something obvious here. Hope You can kick me to right direction.