Fancy Walking category grid

//Custom categories listing Walker
class Post_Categories_Grid extends Walker_Category {

    // Displays start of a level. E.g '<ul>'
    // @see Walker::start_lvl()
    public function start_lvl(&$output, $depth=0, $args=array()) {
        $output .= "\n<ul class='row'>\n";
    }

    // Displays end of a level. E.g '</ul>'
    // @see Walker::end_lvl()
    public function end_lvl(&$output, $depth=0, $args=array()) {
        $output .= "</ul>\n";
    }

    // Displays start of an element. E.g '<li> Item Name'
    // @see Walker::start_el()
    public function start_el(&$output, $category, $depth=0, $args=array()) {
        $link = esc_url( get_term_link( $category ) );
        $image = "<img src='".cfi_featured_image_url( array( 'size' => 'medium', 'cat_id'=>$category->term_id ) )."' />";
        $output .= "<li class='product col-xs-6 col-md-4'><a href='$link' >$image<h3>".strtoupper(esc_attr($category->name));
    }

    // Displays end of an element. E.g '</li>'
    // @see Walker::end_el()
    public function end_el(&$output, $category, $depth=0, $args=array()) {
        $output .= "<mark class='count'>(".esc_attr($category->count).")</mark></h3></a></li>\n";
    }
}


function estlita_category_list($args = array()){
    $categories = get_the_category();
    $category_id = $categories[0]->cat_ID;
    $args = array(
        'show_count'=>true,
        'exclude'=>'1',
        'depth'=>1,
        'use_desc_for_title'=>true,
        'style'=>'',
        'child_of'=>$category_id,
        'walker'=> new Post_Categories_Grid()
    );
    echo "<ul class='products row'>";
    wp_list_categories($args);
    echo "</ul>";
}