How to use Bootstrap in Rails 6

Step 1: Install Bootstrap

yarn add bootstrap

Step 2: Install Bootstrap dependencies: jQuery and popper.js

yarn add jquery popper.js

Step 3: Import JavaScript Bootstrap and dependencies

# app/javascript/packs/application.js
import "jquery";
import "popper.js";
import "bootstrap";

Step 4: Import CSS Bootstrap

Add a folder name stylesheets in app/javascript/

Add application.scss file in app/javascript/stylesheets

Add below code to import bootstrap css:

# In app/javascript/stylesheets/application.scss
@import "~bootstrap/scss/bootstrap"; 

Import CSS to application.js

# In app/javascript/packs/application.js
import "../stylesheets/application" 

DONE!

See folder structure

app/javascript
├── channels
├── packs
│   └── application.js
└── stylesheets
    └── application.scss

More details in Luanotes.com: https://luanotes.com/blogs/using-bootstrap-with-webpacker-in-rails-6