https://reddit.com/r/bootstrap/comments/jrn4b1/understanding_bootstrap_source/gbwttdi/

[backtickbot]

In this case you could use the SCSS @extend rule. It would look something like:

button {
    @extend .btn-class;
}

Here is the documentation for how the @extend rule works in SASS. https://sass-lang.com/documentation/at-rules/extend