That might depend on whether you’re using the Vision or Perspective module. Are you using Vision or are you using Perspective?
I want to say that gradients are not a possibility in Vision (but if someone wants to correct me, feel free).
Perspective gradients are easy:
Set Button.props.style.backgroundImage to linear-gradient(to right, yellow , green).
To do a left-to-right gradient.
For a more diagonal gradient, use something like linear-gradient(to bottom right, red , blue).
This page has some more examples: CSS Gradients.