how to make gradient color for IE8 using sass mixin

@mixin gradient($from-color, $to-color) {
    background-color: mix($from-color, $to-color); /* Fallback */
    background-image: -webkit-gradient
      (linear, 0% 0%, 0% 100%, from($from-color), to($to-color));
    background-image: -webkit-linear-gradient
      (top, $from-color, $to-color); 
    background-image:    -moz-linear-gradient
      (top, $from-color, $to-color);
    background-image:     -ms-linear-gradient
      (top, $from-color, $to-color);
    background-image:      -o-linear-gradient
      (top, $from-color, $to-color);
    -ms-filter: "progid:DXImageTransform.Microsoft.gradient
      (startColorStr='#{$from-color}', EndColorStr='#{$to-color}')";
}

don't forget # of startColorStr='#{$from-color}'