app/assets/stylesheets/rails_admin/custom/mixins.scss
/*
Customize Sass mixins from Twitter-Bootstrap/RailsAdmin theme or add new ones for your own use.
Copy this file to your app/assets/rails_admin/custom/mixins.scss, leave this one untouched
Don't require it in your application.rb
Available mixins to use/override:
https://github.com/twbs/bootstrap-sass/tree/master/assets/stylesheets/bootstrap/mixins
https://github.com/railsadminteam/rails_admin/blob/master/src/rails_admin/styles/base/mixins.scss
Plus the ones from your theme.
*/