// ----
// Sass (v3.4.12)
// Compass (v1.0.3)
// ----

@mixin some-mixin($margin: 10px, $border: null) {
  width: 100%;
  margin: $margin;
  border: $border;
}

.default {
  @include some-mixin;
}

.with-border {
  @include some-mixin($border: solid 1px #000);
}

.without-margin {
  @include some-mixin($margin: null);
}