@mixin mask-image($img, $repeat: no-repeat){
   @include experimental(mask-image, image-url($img), -webkit, -moz, -o, -ms);
   @include experimental(mask-repeat, $repeat, -webkit, -moz, -o, -ms);

   width: image-width($img);
   height: image-height($img);

 }

 @mixin selection($bg, $color: inherit, $text-shadow: none){

   * {

     &::-moz-selection { background: $bg; color: $color; text-shadow: $text-shadow; }
     &::-webkit-selection { background: $bg; color: $color; text-shadow: $text-shadow; }
     &::selection { background: $bg; color: $color; text-shadow: $text-shadow; }

   }
 }
 
 @function text-color($color, $dark: dark, $light: light){
   $text-color: ( (red($color)*299) + (green($color)*587) + (blue($color)*114) ) / 1000;
   $text-color: if($text-color >= 150, $dark, $light);
   @return $text-color;
 }