How to declare a context of of the same component?

.component ~The selector you want to insert .componentThe element you want to style

See example

.btn ~The selector you want to insert .btnThe element you want to style

SASS

+component('.btn')
  +register
    +context('.btn ~')

  +default
    display: inline-flex

  +context('.btn ~')
    margin-left: 0.5em

CSS

.btn {
  display: inline-flex;    
}

.btn ~ .btn {
  margin-left: 0.5em;
}

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