I really like this post by Nathan Curtis where he discusses how buttons can be applied to a design system:
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I love buttons. I can do things with buttons. Take a next step. Make a commitment. Get things done. With buttons, interaction springs to life.
That’s why Buttons are arguably a design system’s most important component. Devilishly simple, they offer a simple label in a defined region I can press. As such, buttons are where you apply a design