Composable CSS using Sass @extend

button.css.scss

@import 'bootstrap';
@import 'font-awesome';

.button {
  @extend .btn;
  @extend .btn-default;
  @extend .btn-large;

  &.destroy {
    @extend .fa;
    @extend .fa-trash-o; /* trashcan icon */
  }
}

samples.html

<!-- Two identical links: -->

<a href="#" class="btn btn-default btn-large fa fa-trash-o">Destroy</a>

<a href="#" class="button destroy">Destroy</a>