Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.4.3)
// Compass (v1.0.1)
// ----

@mixin linear-gradient($fromColor, $toColor) {   
  background-color: $toColor; /* Fallback Color */  
  background-image: -webkit-gradient(linear, left top, left bottom, from($fromColor), to($toColor)); /* Saf4+, Chrome */  
  background-image: -webkit-linear-gradient(top, $fromColor, $toColor); /* Chrome 10+, Saf5.1+, iOS 5+ */  
  background-image:    -moz-linear-gradient(top, $fromColor, $toColor); /* FF3.6 */  
  background-image:     -ms-linear-gradient(top, $fromColor, $toColor); /* IE10 */  
  background-image:      -o-linear-gradient(top, $fromColor, $toColor); /* Opera 11.10+ */  
  background-image:         linear-gradient(top, $fromColor, $toColor); 
}

%fu { 
  @include linear-gradient(red, blue);
}

.btn-1 {
  @extend %fu;
}
.btn-2 {
  @extend %fu;
}
.btn-3 {
  @extend %fu;
}
.btn-4 {
  @extend %fu;
}

SassMeister-output.css

.btn-1, .btn-2, .btn-3, .btn-4 {
  background-color: blue;
  /* Fallback Color */
  background-image: -webkit-gradient(linear, left top, left bottom, from(red), to(blue));
  /* Saf4+, Chrome */
  background-image: -webkit-linear-gradient(top, red, blue);
  /* Chrome 10+, Saf5.1+, iOS 5+ */
  background-image: -moz-linear-gradient(top, red, blue);
  /* FF3.6 */
  background-image: -ms-linear-gradient(top, red, blue);
  /* IE10 */
  background-image: -o-linear-gradient(top, red, blue);
  /* Opera 11.10+ */
  background-image: linear-gradient(top, red, blue);
}