Custom 404 page rails

I am beginner in ruby and cant find solution how to create custom 404-401 page in Rails 5. Any suggestion? I've created a controller "ErrorPages" with action "page_404". Help me please.

Try this:

class ApplicationController < ActionController::Base
  rescue_from ActiveRecord::RecordNotFound, with: :on_record_not_found
  rescue_from AbstractController::ActionNotFound, with: :on_record_not_found
  rescue_from ActionController::RoutingError, with: :on_routing_error
  rescue_from CanCan::AccessDenied, with: :on_access_denied

  def render_404
    if params[:format].present? && params[:format] != 'html'
      head status: 404
    else
      render 'application/404', status: 404
    end
  end

  def on_access_denied
    if params[:format].present? && params[:format] != 'html'
      head status: 401
    else
      render 'application/401', status: 401
    end
  end

  def on_record_not_found
    render_404
  end

  def on_routing_error
    render_404
  end
end

routes.rb

Rails.application.routes.draw do
  get '*unmatched_route', :to => 'application#render_404'
end

/app/views/application/404.html.slim

.content
 .row
  .col-md-12
    h1 404