cab: use btn-tertiary with background

[spike-rabbit]

As discussed in the UX ct meeting:
The content-action-bar should use btn-tertiary with a background instead of custom styling.

Needs to be ajdust in figma as well.

[panch1739]

@spike-rabbit I have done a mockup in Figma to illustrate how it can work. I dont think i can actually build the figma component like that, because it becomes too hard to manage, but i think is irrelevant since it would look the same. Reach out so i can share it.