How to change frontend in Spree commerce (Ror)?

Question

Ruby on Rails

I myself did not expect that I would encounter difficulties when creating my own theme. I found a similar question in Google questions, but the solution is given there 50/50 https://groups.google.com/forum/#!topic/spree-user...
I myself am switching from php to ruby ​​(for self-development). Ruby's logic has not yet fully felt.
How to create your own theme for Spree commerce? Where are the views hiding? In the views folders, the application.html.erb file with the following content:

<title>Spshop</title>
  <%= stylesheet_link_tag    'application', media: 'all', 'data-turbolinks-track' => true %>
  <%= javascript_include_tag 'application', 'data-turbolinks-track' => true %>
  <%= csrf_meta_tags %>

I know that you can override the styles of an existing theme, but my layout is significantly different from the default one, even though it is also on a bootstrap grid.