Bootswatch theme not working correctly

Check for the compatible verison of the Bootswatch page

1) https://bootswatch.com/

2) https://bootswatch.com/3/

Try these both. One of them should work

The problem was that the version of bootstrap used in the default mvc-templates and version of bootswatch themes didn't correspond.

I fixed it by dowloading a compatible theme from this link https://bootswatch.com/3/

The easiest will be to downgrade to boostwatch that's based on bootstrap3, bootswatch.com/3 , or alternatively you can update the html with the new bootstrap4 directives

Thanks to StaticBeagle for hist quick answer!