How to declare a component with :where() condition?

.componentThe element you want to style:where(.condition)The selector you want to insert

SASS

+component('.btn:where(button)')
  +register
    +variant('.new')

  +default
    display: inline-flex
    font-size: 1em

  +variant('.new')
    font-size: 2em

CSS

.btn:where(button) {
  display: inline-flex;
  font-size: 1em;
}

.btn:where(button).new {
  font-size: 2em;
}

More info: +variant, +default, +register, +component