Implement global CSS styles

[vickonrails]

Is your feature request related to a problem? Please describe.
emotion has a way to implement global CSS, but it's not implemented in avocado. A typical use case is for CSS Resets. Most design system libraries come with their own CSS normalize/reset out of the box. I think a good way to implement it would be global CSS in emotion.

Describe the solution you'd like
A way to define CSS values that cascade throughout the design system and the user's application.

Describe alternatives you've considered
Using design tokens in Javascript. But this option won't be perfect because they don't cascade.

Additional context
Emotion has a section on global styles