Today I learned:

You are free to pass a HASH to a flash message. Not just a string 😀

# app/controllers/posts_controller.rb
flash[:post_status] = "Success. Post created" # a string
flash[:post_status] = { title: "Success", subtitle: "Post created" } # a hash!

# app/views/shared/_flash.html.erb
<% flash.each do |type, message| %>
  <%= type %>
  <%= message[:title] %>
  <%= message[:subtitle] %>
<% end %>

You can also register new flash types with add_flash_types

# app/controllers/application_controller.rb
class ApplicationController < ActionController::Base
  add_flash_types :toast

This lets you use

-redirect_to root_path, flash: { toast: "success" }
+redirect_to root_path, toast: "success"