TemplateNotFound: templates/includes/custom.css (frappe theme)

I have installed frappe-theme after installing frappe.
Then on bench start it is throwing the following error.

jinja2.exceptions.TemplateNotFound
TemplateNotFound: templates/includes/custom.css

Anyway I have commented line 11 of “frappe-bench/apps/frappe_theme/frappe_theme/templates/base.html”

{# <style>{% include "templates/includes/custom.css" %}</style> #}

My Question is : Why this custom.css have been included here…Does it have any custom css related to frappe-theme or is it for the user to add his own css in it?

frappe_theme is not a standalone app, it needs custom.css from another app.