Interfaces built with FAST adapt to your design system and can be used with any modern UI Framework by leveraging industry standard _Web Components_.
The important word here is Web Components, which are like React or Vue components but using only standard HTML and JavaScript (no frameworks).
I guess you could even add Bootstrap on top of Fast.
Some references:
- https://en.wikipedia.org/wiki/Web_Components
- https://developer.mozilla.org/en-US/docs/Web/Web_Components
- https://developers.google.com/web/fundamentals/web-component...
- https://caniuse.com/#search=components
Also worth reading: https://dev.to/richharris/why-i-don-t-use-web-components-2ci... (discussion on HN: https://news.ycombinator.com/item?id=20232628)