Add css class to rails link_to helper

You have a syntax problem. Try this instead:

<%= link_to "Learn More", {controller: "menus", action: "index"}, class: "btn btn-inverse" %>

Some documentation for you to go further with the link_to Helper

They say:

Be careful when using the older argument style, as an extra literal hash is needed:

link_to "Articles", { :controller => "articles" }, :id => "news", :class => "article"
# => <a href="/articles" class="article" id="news">Articles</a>

Leaving the hash off gives the wrong link:

link_to "WRONG!", :controller => "articles", :id => "news", :class => "article"
# => <a href="/articles/index/news?class=article">WRONG!</a>

---

I recommend you to use the URL helper generated following your routes configuration. In your case:

link_to "Learn More", menus_path, :class => "btn btn-inverse"

A little reminder on the Helpers generated:

# routes.rb
resources :users

# any view/controller
users_path #=> /users
edit_user_path(user) #=> /users/:id/edit
user_path(user) #=> /users/:id  (show action)
new_user_path(user) #=> /users/new

Try new argument convention:

<%= link_to 'Learn More', 'menus#index', class: 'btn btn-inverse' %>

if you do not have a controller action / route necessary for the link, you can pass nil as the placeholder and get the classes to apply as necessary

<%= link_to 'link verbiage', nil,  class: 'classes for action tag'%>