Views (HTML)
If you want to add a new HTML page, you can do this by working as a regular Rails application.
If you want to override a view given by Decidim you can do this by
change any page HTML you can just find the correct file under the app/views folder and put a copy at app/views/custom keeping as well any sub-folder structure, and then apply your customizations. For example if you want to customize app/views/pages/conditions.html you'll have to make a copy at app/views/custom/pages/conditions.html.erb (note the pages subdirectory).