The design system and libraries are the best way to ensure standardized look and feel to any UI, especially those that are spread across multiple tools like at Hyphen. If built well, they can also be the source of truth and supercharge your design team's ability to move quickly at high fidelity.
To ensure a high degree of consistency across our tools, and to facilitate highly rapid design delivery, I've been creating a procedural and responsive design system for the company. The libraries and the assets within them have live dependencies on one another. An update in one place will update everywhere else. This is true for the "atoms" that are the core of each component and their variations, the patterns that use those components, and the screens that use the patterns.
The design system, as well as anything that doesn't quite fit in a Figma file like interactions or motion guidance, is documented like anything else.
This is an sample of the documentation around motion and interactions. Each of the visuals is actually a gif to clearly communicate design intent to the software team. Detailed specifics are also called out where applicable.