style_capsule

https://github.com/amkisko/style_capsule.rb

Provides component-scoped CSS encapsulation using [data-capsule] attributes for Phlex components, ViewComponent components, and ERB templates. Styles are automatically scoped to prevent leakage between components. Inspired by component-based CSS approaches like Angular's view encapsulation and CSS modules. Works with Rails and can be used standalone in other Ruby frameworks (Sinatra, Hanami, etc.) or plain Ruby scripts.