<%= content_tag :div, class: "#{block.model_name.singular.dasherize} block" do %>
  <%= render "blocks/#{block.model_name.singular}/show", block: block %>
<% end %>

<%= content_tag :div, class: "#{block.model_name.singular.dasherize} block #{block.try(:css_class)}" do %>
  <%= render "blocks/#{block.model_name.singular}/show", block: block %>
<% end %>

Enable adding additional css classes to block wrapper
Enable adding additional css classes to block wrapper
