Keyframes mixin

keyframes.scss

@mixin keyframes($animation-name) {
  @-webkit-keyframes $animation-name {
    @content;
  }
  @-moz-keyframes $animation-name {
    @content;
  }  
  @-ms-keyframes $animation-name {
    @content;
  }
  @-o-keyframes $animation-name {
    @content;
  }  
  @keyframes $animation-name {
    @content;
  }
}

@mixin animation($str) {
  -webkit-animation: #{$str};
  -moz-animation: #{$str};
  -ms-animation: #{$str};
  -o-animation: #{$str};
  animation: #{$str};      
}

usage.css

@include keyframes(slide-down) {
  0% { opacity: 1; }
  90% { opacity: 0; }
}

.element {
  width: 100px;
  height: 100px;
  background: black;
  @include animation('slide-down 5s 3');
}