Steps to reproduce the issue

create secondary button in backend and hover
<button type="button" class="btn btn-secondary">Secondary</button>

create outline-secondary button in backend
<button type="button" class="btn btn-outline-secondary">Secondary</button>

Expected result

all variables should be defined

all outline buttons should have same style

Actual result

light theme (--btn-secondary-color-hvr, --btn-secondary-bg-hvr):

dark theme (--btn-secondary-color-hvr):

secondary outline button is not outline:

Additional comments

similar #43117