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

//.element {
    //  @include animation('slide-down 5s 3');
// }
@mixin animation($str) {
    -webkit-animation: #{$str};
       -moz-animation: #{$str};
        -ms-animation: #{$str};
         -o-animation: #{$str};
            animation: #{$str};      
}