Kinvart - There are two things to modify. I should have shown in the example that you need to use stylesheet_chcategories_dressing.css (you would best delete stylesheet_categories_dressing.css to avoid confusion), and replace #categories with #chcategories in the examples.

The classnames after you do the "special" mod will be different than I showed, because I was working from the next unreleased version of Cat Dressing which uses slightly different methods. Your top categories now have class names like .cat-category-moski, so you want the stylesheet to reflect this.
Code:
/*example for custom individual category styling*/
#chcategories li.cat-category-moski a {
    background-image: url(../images/moski_bg.gif);
    background-repeat: none;
    padding: 2px 0 2px 23px;
    }

#chcategories li.cat-category-otroski a {
    background-image: url(../images/moski_bg.gif);
    background-repeat: none;
    padding: 2px 0 2px 23px;
    }

/*example for custom category group styling*/
ul#catGroup9 { /*moski*/
    background-color: #bbeeff; 
    }