I create my own personal systems when creating a design.

For example, I like to choose 2 or 3 different sizes of padding and margin for elements on the page. Similar elements get the predefined padding or margin - no guessing.

Navbar will have the same amount of space between the navlinks as the x-padding of the entire navbar content.

Spacing above and below the navlinks will be equal to the spacing between the navlinks, and the x-padding of the nav content.

If there is a container below the nav, there will be the same equal amount of space dividing the two components.

This creates a symmetrical and beautiful design, especially when applied throughout the entire project.

So I would say a design system, for me, is strategically reusing your predefined design components