In the UI consider using a less-subtle color for the Cancel/Previous buttons

[somascope]

What problem does this feature solve?

Once I learned where the Cancel button was, this was not as much of an issue, but initially I couldn't see where it was. On one hand, I appreciate the subtly of these buttons, but it did make the initial discovery of them by a new user slower than it could be.

What does the proposed API look like?

This is a UI suggestion, nothing to do with API.

[Akryum]

You mean add a background color to them?

[rubenmoya]

If you mean this one:

for me is more a position problem than a color one, I think putting both the next and cancel buttons together would make a huge difference.

[Berkmann18]

It's indeed not very UX friendly, I can understand the green/lime theme applied to buttons but usually, users (mainly new ones) would expect it to be more noticeable, in other words, red-ish and closer to the "click zone" (I can't remember the exact UX term that describes the area of an app where the user would focus his/her attention more in regards to buttons).