My team develop an angular 5 application that has been in production for a while, but we\'ve been tasked recently with making the app work in other 3 sites the company owns.
I believe the Angular 6 Elements is going to be your only option for the non-angular apps. That is the only method that I am aware of that allows components to be executed outside of angular.
In order to maintain your style encapsulation, you can use the css prefix:
:host
in your component's .css or .scss files.
If you can get rid of the non-angular requirement, I would recommend the Angular CDK PortalHost and DomPortalHost.