dev said over 1 year ago on Slim Select with Stimulus :
Rails 7 with importmap
1) in Terminal
bin/importmap pin slim-select
or
bin/importmap pin slim-select --download 

2) Add css (3 variants)
- add to app/views/layouts/application.html.erb
<%= stylesheet_link_tag "https://cdnjs.cloudflare.com/ajax/libs/slim-select/1.27.1/slimselect.min.css", "data-turbo-track": "reload" %>
or
- in rails console
`curl https://cdnjs.cloudflare.com/ajax/libs/slim-select/1.27.1/slimselect.min.css --output "#{Rails.root.join('app', 'assets', 'stylesheets')}/slimsel
ect.min.css"`
or
- add to app/assets/stylesheets/application.css
@import url("https://cdnjs.cloudflare.com/ajax/libs/slim-select/1.27.1/slimselect.min.css");