Mixins for Animating Between Gradients

gradient-animation.less

.gradient-animation( @start, @end, @transTime ){
  background-size: 100%;
  background-image: linear-gradient(@start, @end);
  position: relative;
  z-index: 100;
  &:before {
    background-image: linear-gradient(@end, @start);
    content: '';    
    display: block;
    height: 100%;
    position: absolute;
    top: 0; left: 0;
    opacity: 0;
    width: 100%;
    z-index: -100;
    transition: opacity @transTime;
  }
  &:hover {
     &:before {
       opacity: 1; 
     }
  }
}

gradient-animation.scss

@mixin gradient-animation( $start, $end, $transTime ){
  background-size: 100%;
  background-image: linear-gradient($start, $end);
  position: relative;
  z-index: 100;
  &:before {
    background-image: linear-gradient($end, $start);
    content: '';    
    display: block;
    height: 100%;
    position: absolute;
    top: 0; left: 0;
    opacity: 0;
    width: 100%;
    z-index: -100;
    transition: opacity $transTime;
  }
  &:hover {
     &:before {
       opacity: 1; 
     }
  }
}