--#{$variable-prefix}btn-padding doesn't exist so the custom sizing button with CSS variables is not fully functional.
In this fix, I chose to keep 2 separate vars but it could probably be only 1 var.
Note: there is another bug that can be seen in this page: the last buttons are not vertically aligned with the other buttons in a same row in the examples. It is probably due to the new rule in https://github.com/twbs/bootstrap/commit/37f3977e6d96e274cb73255d99e3e4ec60f03c0f:
> :not(hr):last-child {
margin-bottom: 0;
}
I can create an issue if needed.