module Spree
  module BaseHelper

    def taxons_tree(root_taxon, current_taxon, max_level = 1)
      return '' if max_level < 1 || root_taxon.children.empty?
      content_tag :ul, class: 'taxons_list' do
        root_taxon.children.map do |taxon|
          css_class = (current_taxon && current_taxon.self_and_ancestors.include?(taxon)) ? 'current' : nil
          content_tag :li, class: css_class do
            link_to(taxon.name, seo_url(taxon), :class => "#{current_taxon}") +
            taxons_tree(taxon, current_taxon, max_level - 1)
          end
        end.join("\n").html_safe
      end
    end

  end
end

module Spree
  module BaseHelper

    def taxons_tree(root_taxon, current_taxon, max_level = 1)
      return '' if max_level < 1 || root_taxon.children.empty?
      content_tag :ul, class: 'taxons_list' do
        root_taxon.children.map do |taxon|
          css_class = (current_taxon && current_taxon.self_and_ancestors.include?(taxon)) ? 'current' : nil
          content_tag :li, class: css_class do
            link_to(taxon.name, seo_url(taxon), :class => "taxonomy-child") +
            taxons_tree(taxon, current_taxon, max_level - 1)
          end
        end.join("\n").html_safe
      end
    end

  end
end

Add css class to taxon links.
Add css class to taxon links.
