An example of building design system.
A design system is a sets of principles, standards, conventions, and guidelines that need to be followed religiously in order to bring consistency across a team or product.
A design system set to achieve consistency and if defined in simpler way then it bring consistency to the user interface like buttons, text, icons, colors, spacing, typography, etc.
Another aspect of design system is it reduce the decision making and when developer start to build it already has defined ui to build upon.
Also it helps reduce the gap between the designer and the developer. because every one team are not expecting completely different ui.
No body wants to see hex code spit all over the codebase.