Bootstrap doesn’t do much to naked elements in your markup. It sets the default font and makes a few color changes, but most of what Bootstrap does requires you to add classes to certain elements in a particular way. This means you’ll need access to the markup before you get started.
You might recall that you didn’t write any markup for the login screens—they were all provided by Devise. Devise is packaged as a Rails Engine, so the gem itself contains the views. But it also contains a generator called devise:views that will extract those views into our application, allowing us to modify them.
|||$ bundle exec rails generate devise:views|
|||invoke Devise::Generators::SharedViewsGenerator ...|