Generated by SassMeister.com.

SassMeister-input-HTML.html

<button class="Btn">Just a Button</button>
<button class="Btn--disabled">Disabled Button</button>
<button class="Btn-secondary">Secondary Button</button>
<button class="Btn-secondary--disabled">Secondary Disabled Button</button>

SassMeister-input.scss

// ----
// Sass (v3.4.4)
// Compass (v1.0.1)
// ----

%Btn-base {
  border-radius: 5px;
  padding: 0.5rem;
}

@mixin ColoredBtn($color, $background-color) {
  @extend %Btn-base;
  color: $color;  
  background-color: $background-color;
}

.Btn {
  @include ColoredBtn(white, blue);
  // .Btn--disabled
  &--disabled {
    @include ColoredBtn(white, grey);
  }
  // .Btn-secondary
  &-secondary {
    @include ColoredBtn(blue, white);
  }
  // .Btn-secondary--disabled
  &-secondary--disabled {
    @include ColoredBtn(blue, light-grey);
  }
}

SassMeister-output.css

.Btn, .Btn--disabled, .Btn-secondary, .Btn-secondary--disabled {
  border-radius: 5px;
  padding: 0.5rem;
}

.Btn {
  color: white;
  background-color: blue;
}
.Btn--disabled {
  color: white;
  background-color: grey;
}
.Btn-secondary {
  color: blue;
  background-color: white;
}
.Btn-secondary--disabled {
  color: blue;
  background-color: light-grey;
}

SassMeister-rendered.html

<button class="Btn">Just a Button</button>
<button class="Btn--disabled">Disabled Button</button>
<button class="Btn-secondary">Secondary Button</button>
<button class="Btn-secondary--disabled">Secondary Disabled Button</button>