I have followed the following to install bootstrap 4 into my Angular 2 project: Accepted Answer, following the first 1,2,3 and 4 steps
However when I add the following <
Somebody has created a new version of the template library specifically design for Angular 2+. According to the website, it was developed by ng-team, although the link it gives gets a 404 response. It does work, though, and I have used it in multiple places throughout my current project. You'll just have to pull in the library with npm. All of the instructions are on this website:
http://valor-software.com/ngx-bootstrap/#/
That page shows you all of the install and usage instructions you need to get started. I hope this helps!