@stefanobellu:
A whole lot could be said about your background image, but let me try to make it short. You may then use some of it, as well as try to use other sources for gaining more knowledge of CSS (e.g.
the documentation here
and elsewhere on the web) and using Firebug or another browser console, so you're able to solve this and other display mysteries yourself.
Please note that all CSS here will be limited to this exact product listing only!
To be safe the code works, you should add it at the very end of your HikaShop frontend_custom.css file.
1. Transparency of product thumbnails:
I don't think you want this (as the display would become "overloaded" with imagery, and the product titles very hard to read), but If you want the background image to "shine through" the thumbnails, too, you should try out such CSS:
#hikashop_category_information_module_107 div.hikashop_subcontainer {
background: rgba(0, 0, 0, 0) !important;
}
2. Height of product thumbnails:
Maybe you did so on purpose, but with 300px the height seems quite huge, leaving a lot of white space in between product image and price/title. At least when making the background transparent, you may want to consider reducing it, and you could do so by changing or deleting the "Pane height" value in the settings for the listing (via HikaShop backend), or by applying such CSS:
#hikashop_category_information_module_107 .hikashop_product_image {
height: auto !important;
}
Eventually replace "auto" with a value in pixels.
3. Background image:
Yours is a single large file (almost 2MB !!!), unnecessarily slowing down your pageload. Since it's repetitive content, you should use a smaller file and repeat it with CSS. I'm attaching here a much smaller file which you should use, and I'll make the CSS code accordingly, assuming it'll be in the same location on the server as the one you're using now.
a) The following code will put the image repeatedly under the area marked in your screenshot - as far as I could see there. Note it does cover the pagination, but it won't cover the HikaShop footer and below.
#hikashop_category_information_menu_121 .hikashop_submodules {
background: url("http://www.aswebgraph.com/vet/sfondo50_small.jpg") repeat scroll 0 0 rgba(0, 0, 0, 0);
}
b) By using the following instead, the pagination will be left out and probably remain better readable:
#hikashop_category_information_menu_121 .hikashop_products {
background: url("http://www.aswebgraph.com/vet/sfondo50_small.jpg") repeat scroll 0 0 rgba(0, 0, 0, 0);
}
c) If you wanted to have the background of the entire page covered instead, it'll take some extra "tricks", which would lead too far here...
FYI, I used Firebug to analyse your website and simulate it right there. Again, I recommend you getting your head around this, too.