```ruby
require './config/environment'

class ApplicationController < Sinatra::Base

  configure do
    set :public_folder, 'public'
    set :views, 'app/views'
  end
end
```

Add index route to application controller
user
```ruby
require './config/environment'

class ApplicationController < Sinatra::Base

  configure do
    set :public_folder, 'public'
    set :views, 'app/views'
  end

  get '/' do
    erb :index
  end
end
```
assistant