CSS Bundling for Rails
Use Tailwind CSS, Bootstrap, Bulma, PostCSS, or Dart Sass to bundle and process your CSS, then deliver it via the asset pipeline in Rails. This gem provides installers to get you going with the bundler of your choice in a new Rails application, and a convention to use
app/assets/builds to hold your bundled output as artifacts that are not checked into source control (the installer adds this directory to
.gitignore by default).
You develop using this approach by running the bundler in watch mode in a terminal with
yarn build:css --watch (and your Rails server in another, if you're not using something like puma-dev). You can also use
./bin/dev, which will start both the Rails server and the CSS build watcher (along with a JS build watcher, if you're also using
Whenever the bundler detects changes to any of the stylesheet files in your project, it'll bundle
app/assets/builds/application.css. This build output takes over from the regular asset pipeline default file. So you continue to refer to the build output in your layout using the standard asset pipeline approach with
<%= stylesheet_link_tag "application" %>.
When you deploy your application to production, the
css:build task attaches to the
assets:precompile task to ensure that all your package dependencies from
package.json have been installed via yarn, and then runs
yarn build:css to process your stylesheet entrypoint, as it would in development. This output is then picked up by the asset pipeline, digested, and copied into public/assets, as any other asset pipeline file.
This also happens in testing where the bundler attaches to the
test:prepare task to ensure the stylesheets have been bundled before testing commences. (Note that this currently only applies to rails
test:* tasks (like
test:controllers), not "rails test", as that doesn't load
If your test framework does not define a
test:prepare Rake task, ensure that your test framework runs
css:build to bundle stylesheets before testing commences.
You can configure your bundler options in the
build:css script in
package.json or via the installer-generated
tailwind.config.js for Tailwind or
postcss.config.js for PostCSS.
You must already have node and yarn installed on your system. You will also need npx version 7.1.0 or later. Then:
cssbundling-railsto your Gemfile with
Or, in Rails 7+, you can preconfigure your new application to use a specific bundler with
rails new myapp --css [tailwind|bootstrap|bulma|postcss|sass].
How do I import relative CSS files with Tailwind?
If you want to use
@import statements as part of your Tailwind application.js file, you need to configure Tailwind to use
postcss and then
postcss-import. But you should also consider simply referring to your other CSS files directly, instead of bundling them all into one big file. It's better for caching, and it's simpler to setup. You can refer to other CSS files by expanding the
application.html.erb like so:
<%= stylesheet_link_tag "application", "other", "styles", "data-turbo-track": "reload" %>.
How do I avoid SassC::SyntaxError exceptions on existing projects?
Some CSS packages use new CSS features that are not supported by the default SassC rails integration that previous versions of Rails used. If you hit such an incompatibility, it'll likely be in the form of a
SassC::SyntaxError when running
assets:precompile. The fix is to
bundle remove sass-rails (or
sassc-rails, if you were using that).
CSS Bundling for Rails is released under the MIT License.