How can I change the look of the navigation side bar, to look like this

[paha]

Apply the image as a background image to the element you want it in with css

Interesting Idea,

But I just see that if the links of categories increase or decrease, the image will not feet corectly.

is nost pocible to add an image per link, so it is independet color for each link, category? so if I add a categorie or product the link image or background color will appear with it, or disappear if the category is deleted