There are a few variables in button.scss that aren't defined or are unused:

Variable not defined - this one is a bug in the large (CTA) button font size:
Line 737: --#{$button}--m-display-lg--FontSize is referenced but never defined.
Line 283 defines --#{$button}--m-link--m-display-lg--FontSize (used for link buttons on line 577)
Line 737 references --#{$button}--m-display-lg--FontSize (for non-link display-lg buttons), but this variable is not defined

Variables defined but never used: (determine if needed and use or remove)
--#{$button}__progress--Opacity (line 337) — Defined but never used. The progress element doesn't use opacity.
--#{$button}--m-display-lg--FontWeight (line 282) — Defined but never used. The pf-m-display-lg modifier sets padding and font size but not font weight. (probably goes with the large button text size above
--#{$button}--disabled--BorderColor (line 295) — Defined but never used. The disabled styles use border-color: transparent; directly in the &::after block (line 843) instead of the variable.

Jira Issue: PF-2902