An animation located at Primer Components gives the impression of having been structured within Adobe After Effects, which is a program that supports plugins that expand its features so that it can better allow users to accomplish specific nuances. If a plugin was used in this case, it may have been the Lottie library, which effectively serves as a filter that previously exported After Effects animations are run through so that they can be rendered directly on the client side. In this environment, the animations will enjoy the aforementioned advantages of the SVG format.
Given the simplicity of the animation at Primer Components, however, it is plausible that it was achieved entirely through the suite of syntax that is available within CSS by default. Ideally, a web animation that can be done purely within CSS should not involve more dedicated libraries. For more information click here https://v.redd.it/dnxw7c7ifl631.