Custom CSS not working with CSS Bundling for Rails 7 - ruby-on-rails

Question

Playing around with Rails 7 and I don't understand why my custom CSS is not working.
I built new rails app with flag for Bootstrap, which is working fine (CSS and JS, tested with bootstrap modal). These are my default config files:
application.js
// Entry point for the build script in your package.json
import "#hotwired/turbo-rails"
import "./controllers"
import * as bootstrap from "bootstrap"
application.bootstrap.scss
#import 'bootstrap/scss/bootstrap';
package.json
{
"name": "app",
"private": "true",
"dependencies": {
"#hotwired/stimulus": "^3.0.1",
"#hotwired/turbo-rails": "^7.1.0",
"#popperjs/core": "^2.11.2",
"bootstrap": "^5.1.3",
"esbuild": "^0.14.23",
"jquery": "^3.6.0",
"popper.js": "^1.16.1",
"sass": "^1.49.9",
"stimulus": "^3.0.1"
},
"scripts": {
"build": "esbuild app/javascript/*.* --bundle --sourcemap --outdir=app/assets/builds",
"build:css": "sass ./app/assets/stylesheets/application.bootstrap.scss ./app/assets/builds/application.css --no-source-map --load-path=node_modules"
}
}
And I can built CSS in /builds/application.css
Now I want to add custom CSS. This is my process:
Added new file stylesheets/custom.css, with css:
.my-class {
color: #fff;
background-color: #00eb00;
}
Add import to application.bootstrap.scss
#import "custom";
yarn run build:css
And now I can see .my-class in builds/application.css
But when I try to use id in HTML, no CSS is added. Why? Should I place it somewhere else?
EDIT: I got it running, but only when I run manually rails assets:precompile and then bin/dev.
Why do I need to precompile every time I change something?

Answer 1

In a fresh rails 7 app (with css=bootstrap), here's what I did to get custom css styles:
Uncomment gem 'sass-rails in Gemfile, then bundle install (more info on that here)
Create a new css file in app/assets/stylesheets and name it example.css.scss
Add this line to app/assets/config/manifest.js:
//= link example.css
Wherever you need access to those styles, include this tag
<%= stylesheet_link_tag "example", "data-turbo-track": "reload" %>
Start your server with bin/dev instead of rails server
Everything should work (a nice test is to include this in your example.css.scss file and H1s should turn green)
h1 {
color: green;
}
Resource
Very helpful video here

Answer 2

I just encountered this problem and noticed both JavaScript and CSS are not recompiled after changes.
If you have gem jsbundling-rails included in your gemfile, check out https://github.com/rails/jsbundling-rails for more details and how-tos.
Run yarn run build:css to recompile the CSS assets.
I prefer using ./bin/dev to start my local server and monitor both JavaScript and CSS updates.

Answer 3

It worked for me if I added
//= link custom.css
to app/assets/config/manifest.js
And I didn't add #import "custom"; to application.bootstrap.scss