Why did bootstrap connect to the bitrix site?

Question

1C-Bitrix

I cleared the cache of the site and the layout went.
Error in console

Access to CSS stylesheet at 'https://stackpath.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css' from origin 'http://mysite-bitrix.ms.ru' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: It does not have HTTP ok status.

Google says to submit the title.
But I don't understand how to send it to Bitrix.
And as if everything was fine ... what happened then ?!

Answer 1

Good afternoon!
Bitrix already has Bootstrap, why pull a third-party one?
It lies at the address - /bitrix/js/ui/bootstrap4/
If it exists, you can connect it like this:

use Bitrix\Main\UI\Extension;
Extension::load('ui.bootstrap4');

Answer 2

In the header I write

use Bitrix\Main\UI\Extension;
Extension::load('ui.bootstrap4');

But there are errors in the console.
Bootstrap4 needs to include Popper.js