Generated by SassMeister.com.

SassMeister-input-HTML.html

<div class="block"><h1>hi</h1></div>

<div class="block-blue"><h1>hi</h1></div>

SassMeister-input.scss

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

$primary-color: #000;

.body {
  color: $primary-color;
  
  .title {
    font-size: 3em;
  
    &:hover {
      text-decoration: underline;
    }
  
  }

}

@mixin solidblock($bg){
  // background: $bg;
  background: mix($bg, #fff, 40%);
}

.block {
  @include solidblock(#000);
}

.block-blue {
  @include solidblock(#fff);
}

SassMeister-output.css

.body {
  color: #000;
}
.body .title {
  font-size: 3em;
}
.body .title:hover {
  text-decoration: underline;
}

.block {
  background: #999999;
}

.block-blue {
  background: white;
}

SassMeister-rendered.html

<div class="block"><h1>hi</h1></div>

<div class="block-blue"><h1>hi</h1></div>