Where has .btn-default gone in Bootstrap 4?

Question

According to the Bootstrap 3 to Bootstrap 4 migration docs:

Buttons

• Renamed .btn-default to .btn-secondary.

But

Answer 1

The btn-outline-secondary class in Bootstrap 4 generates the closest to what used to be btn-default in Bootstrap 3.

That seems to be "typo" there in the docs.

primary is the blue button/color and secondary is the grey ones.

And the very light grey is btn-light.

Here's the reference link for Bootstrap 4 buttons:

https://getbootstrap.com/docs/4.0/components/buttons/