Bootswatch theme not working correctly
Check for the compatible verison of the Bootswatch page
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!